Correct Sizing of Residential HVAC Air Conditioning Systems Filter & Ductwork Systems
HVAC Procedures for Proper Ductwork and Filter Sizing for Residential Air Conditioning Systems - TEL ASP FR CFM Air Flow
- with Darrell Udelhoven - HVAC RETIRED - udarrell

Filter sizing: ACCA Manual D requires a low 300-fpm velocity through a new clean cheap fiber glass filter; a 60F temp-rise maximum means the 76,000 will have close to 1200-CFM / 300-fpm is 4-sf * 144 is 576-sq.ins of open-air-filter-area, media type filters only have 60% to 65% open-air-area. 576 * 1.65 is 950-sq.ins of filter area. One 16X25 filter (actually it's 15X24) is 400-sq-ins *2 is 800-sq.ins; still 150-sq.ins less than called for. That is why it's very important to reduce A/C size as much as possible.

Read this pdf explaining what Electric Power Companies are finally instituting: http://bit.ly/1gDxkmf Verified Performance, Get what U pay for!

Above 500-fpm velocity debris blows through a media type filter. One 16X24 filter has a Ak of 1.84 @ 300-fpm it will only flow 552-CFM; @ 650-fpm it will flow 1196-CFM; that is 150-fpm above where debris begins to blow off excessively at 500-fpm velocity through the filter. Hart & Cooley Filter Engineering Data using media type filters. A 1″ deep pleated filter has way too much pressure drop resistance, use 4" or 5″ deep pleated filters !

Please Respond on my Blog; let me know if you can't post: Ballpark Checking A/C Performance
Best ROI Investment or Lose the Investment money annually "Home Energy Efficiency Pays You BIG." Video

More authenticated survey test corroboration; the surveyed HVAC systems were systems that they had complied with their program’s energy standards and "all had received substantial incentive payments," but delivered an average of only 63% of their Rated Btu/Hr to the homes & 50% of the required airflow. http://bit.ly/1adKKG6 - We can fix these costly problems!
70% of homes in California are operating at 50% capacity. - California Energy Commission - We can fix these problems!
http://www.law.cornell.edu/uscode/text/47/396 (8) public television and radio stations and public telecommunications services constitute valuable local community resources for utilizing electronic media to address national concerns and solve local problems through community programs and outreach programs...
Example of typical furnace over-sizing; my former oil furnace & the other house here on the farm both had 140,000-Btu/hr input oil furnaces installed when new they were 80% efficient; 140,000 * .80% is 112,000 * an 85% nozzle is 95,200-Btuh.
The homes both load-calc Design at -15F between 26,000 to 32,000-Btuh; therefore a 38,000- Btuh will easily handle the heat-loss at any extreme temperature. 95,200-Btuh / 38,000-Btuh is +2.5 times the proper Btuh sized furnace. 38000 * 2.5 is 95,000; left the fractions off the 2.5...
 

Totally Free Load-Calc
This Free online calc will help you determine equipment sizing & point-out areas that need efficiency retro-work - Once you calculate the page it saves the inputs for up to 24 minutes or, until you change inputs or close your browser.

We could reduce existing residential heating Btu per hour SIZING by around 50% and cooling equipment SIZING in America by 30% to 40% or more if Contractor's would perform honest Manual J calculations and provided full credit for every load reducing element or detail they can when doing the calculation audit.

Load reduction remedial actions should always be provided as options toward further reducing Air Conditioning and heating equipment sizing.

You can experiment with changing the design temperatures in both heat & cooling, (or start-over showing the New Retro-R-Values) also to see whether the equipment exceeds, at those particular temperatures & new retro conditions, (exceeds) the Btuh calculation load numbers, 'in each' of the 3 cooling categories; Total Btuh, Sensible Btuh & Latent Btuh.

Using Goodman Manufacturing or other Expanded Cooling Data; e.g., using a 2-Ton 13-SEER, R410A, @75F 50%RH Indoors; "outdoor 90F," 'interpolate' between Charts 85F & 90F ambient, @800-CFM Mbh is 21.55, S/T is .765 * 21,550 is16,486-Btuh Sensible; 21,550 - 16,486 is 5,064 Latent. That's the simple close enough math...

MY HVAC BLOG - YOUR QUESTIONS & COMMENTS WELCOME *Use for listing test data required for effective trouble-shooting!

HVAC Efficiency Overview My "HVAC Service Procedure AUDIO," Overview; listen while doing other things

Spreadsheet load-calcs 1/2Ton Cools Mine: Darrells-house-Heat-gain 1st Floor (1).pdf  | Dons-House -Heat-gain room detailed HTMs7613.pdf
Local Contractor Locater Map - Find These Contractor PROs in your area

Figuring Delivered BTUH  SIMPLE BTUH AIRFLOW MATH | Formula for finding CFM Airflow

*Basics Featuring Testo 556 >Video Testo 550 Features

*Video checking static ESP*Video 2 checking static ESP View!Got DSL 11/2010
*Video measuring airflow Velocity - Vane anemometer on a Return Air grille
I'd use close to .50% for the free-area of a clean FILTER, & .90% factor for open grille area. He programmed it in, because when I did the math using .90% for the grille, I got 336.57863-FPM Vel *X 2.376562-SF free-air-area= 799.9-CFM, or 2-Ton of airflow.
 
Testo 605-H2 Fast Accurate Wet Bulb

Why Look at your Ducts (Leakage up-to 33% of cooling cost) when replacing your AC System; a must viewing:
http://www.youtube.com/watch?v=IV0Rwv5gco4

CFM & FPM Velocity Sizing MERV 8 Pleaded Filters 
1” deep M-8 filter’s rated at 175 fpm medium and 350 fpm high; A 16X20 1" MERV 8, Rated @ only 780-CFM
*Selecting Air Filters - Sizing the Filtering Area - * Filter Data  *Critically important!
Comparative Tests Concerning Pressure Drops of HVAC Filters - Important Criteria!
At 300-fpm, the 4" deep Merv 7 has the same pressure drop at .10 of an inch, as the 1" fiber glass filter; all filter areas were 24X24
AIRFLOW DIAGNOSTICS and REPAIR PDF  Excellent & thorough PDF Slide Views
Low Priced Affordable Infrared Camera
Fieldpiece SMAN3 Digital Manifold Gauges PDF

Home Energy Audits - Rochester, NY Area Real Energy Cost Savings - Ted Kidd
Home Energy Efficiency Auditing procedures etc HVAC-Talk Thread
I Salute this AZ HVAC Website
company logo is a triskelMO Home Energy Audits LLC
Why Home Energy Efficiency Auditing is important to our future Jeremy Rifkin Video
COMFORT INSTITUTE Consumer Protection Division Found 04/14/12 What I've been saying!
Do a Search for a Comfort Institute HVAC Contractor 'Member' in your zip code

More HVAC Videos at bottom of this & other pages

HVAC TALK HVAC Talk Community Ask the Experts FREE Forum - Save Money!

HVAC-TALK GENERAL DISCUSSIONS - OPEN FORUM
Importance of Two-Way Communications with HVAC Customers

ENERGY EFFICIENCY AUDITOR TALK FORUM - This is the future of the HVAC field of work

I found this new Video confirmation today of my mass communication ideas, 03/05/12; VIEW ALL of this New VIDEO:
THE CONVERGENCE OF COMMUNICATIONS & ENERGY a world changing video about everyone's future, by Jeremy Rifkin View this Video it opens a future of unlimited economic opportunities...

Customers

*Sizing Units to Existing Duct Airflow | Figuring Delivered BTUH |* HEAT PUMP DIAGNOSTICS 
 Ductwork Retrofitting Graphed Blower-Curve-Chart |* Return Air - External Filter-Grille Sizing |
Measuring Low Airflow!
 *Duct & Diffuser Sizing|
|* HEAT PUMP DIAGNOSTICS

Air Infiltration Sources Up-to 50% of Load 
ROOM-DUCT CFM - Formula for finding CFM |
MAIN ONLY DUCT SIZING CHART

*MAIN & BRANCH DUCT CHART  | Square Inches to Round Duct & More |
 
DUCTWORK BASICS  |
Basic AC Overview - Specifications VS. Reality  |

TEL - Solving for ASP Available Static Pressure
 >Use Manual D Duct Design
Oil Furnace Airfow Problems HVAC-Talk FORUM @#10

 
TXV or Piston Test | System Evacuation Procedures
| SA/RA locations | Gurgling@TXV | Sealing Rim Joists

*
Condensing Temp CT
| ACCA ENERGY STAR pdf  | IWC_to_Pascals
Government initiated Energy Audits from CNN audio listen to while reading - CNN
Residential Quality Installation Check List Pre-qualify H-VAC Contractors
Everything You need to know about HOME INSPECTIONS

I'd always begin with a thorough Home Energy AUDIT that shows all the options for lowering the heat-gain & heat-loss, then after reducing air infiltration, etc., have a room by room manual J heatload calc performed. A reduction in equipment sizing will usually greatly improve the duct system performance.

This is where the greatest savings in both heating & cooling will accrue; this will help in the down-sizing of equipment.     

"The 'proper heatload' on the evaporator coil must be established"
Check and thoroughly seal all the ductwork! For efficient operation, always check the return air temperature at the blower & at the Return Air Grille(s) to know whether it is drawing hot air from the attic or garage areas.

What I stated above, that ought to be done is far more important than SEER rating; as that will determine the SEER achieved & the energy savings.

Then do a manual J room by room heat-gain calc with the option shown so you can do everything possible to reduce all sources of heat-gain & heat-loss, greatly reducing both heat & cooling BTUH equipment sizing.

Before you do anything else, educate yourself enough to "ensure that you request the proper things be done in the proper order of sequence." Checking ductwork & Airflow Checking Static Pressures  is Critically Important. As is knowing the operating feet per minute (FPM) velocity, the CFM & BTUH to each room along with the Total CFM airflow & BTUH.

The critical importance of selecting the proper equipment components for your climate zone

It is essential to understand why the local weather environment dictates what SEER level air conditioning equipment you should choose.

In choosing equipment and its SEER level, it is important to understand the design engineering behind its functional capabilities.

First, when the engineers designed for higher Seer levels, they increased the volume and the BTU per hour capacity of the condenser coils and the evaporator coils; however, they reduced the BTU per hour capacity of the compressor.

The volumetric capacity of that smaller compressor depends on the absolute suction and discharge pressures under which the compressor is operating. The higher SEER units also have a much larger quantity of refrigerant charge than the older 10 & 12-SEER units had.

The lower volumetric capacity ratio of the compressor to the higher coil capacities only works well in an 82F laboratory weather environment with a 50% relative humidity level,which is never a stable operating condition in the real world environment.

When you select the high Seer units in a climate where you have high outdoor sensible temperatures along with a high humidity, the temperature pressure ratio of the evaporator coil skyrockets as does the condenser coil pressures and temperatures, therefore the smaller capacity compressor in its relationship to the coils becomes overloaded.

Here comes the engineering caveat, if you are in a high temperature high humidity climate zone the evaporator pressure temperature ratio will be so high that there will be very little condensation of the moisture in the air. Additionally, always select an evaporator coil with a TXV thermostatic expansion valve refrigerant metering device as it will keep the coil colder at varying lower outdoor temperature conditions.

Also, buy a digital programmable room T stat that also has a cycles per hour (CPH) or a swing setting from 1 to 9 so you can reduce the number of short cycles while increasing the runtime of each cycle. This can really increase SEER performance & help a lot to control humidity problems in the summer cooling mode.

Additionally, the volumetric capacity of the smaller compressor will not be able to handle the increased volume of vapor. Added to this the condensing pressure will be much higher with also reduces the volumetric capacity of the compressor which is rated at less than the BTU per hour of both coils.

The higher SEER level you select above the 13 or 14-SEER levels the ratio between the lower BTU per hour capacity of the compressor compared to the evaporator and condenser coils becomes worse. Therefore, if you are located in a hot or, a hot and humid climate from an engineering standpoint and a performance standpoint, I do not believe it is a wise decision to go to extremely high SEER rated equipment.

There may be rare exceptions to the above statements, if a variable speed compressor and variable speed blower motors are used. When these components are used, you should make sure that the contractor proves to you, before you buy the equipment, that the combination of components will work properly in your climate zone.

Find the best way to save energy in your home, use your zip code. Profitabiity of Energy efficiency Upgrades | Hidden cost of Home energy Use

Then have a manual "J" heat-gain / heat-loss load calc done, followed by a manual "S" for equipment sizing & then a manual "D" for proper ductwork sizing.  All registers, grilles, filter racks, & diffusers must be located & sized for optimal efficient performance of the system. Order Turning Vanes for long radius 90-ells; use long radius 45's.
The correct sizing of residential air conditioning systems & ductwork is crucial to ensuring proper indoor space conditioning, equipment performance, and economical operation. Unfortunately, many A/C contractors measure “correct equipment sizing” by the system's ability to meet any indoor thermostat setting at any outdoor temperature. That method of sizing will lead to inefficient operation for the vast majority of conditioning time. Air conditioning systems “must be sized to meet typical or average indoor and outdoor conditions to ensure proper air mixing, filtration and dehumidification of indoor air across seasonal variations.”
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A Major Oil Furnace Airflow Problem Fix
Regal & Hallmark & nearly all Oil Furnaces - Installation manuals
http://www.boyertownfurnace.com/ProductDocuments/index.aspx
Download the installation & service manuals from ABOVE LINK BELOW LINK MAY NOT WORK!
http://www.boyertownfurnace.com/ProductDocuments/HallmarkONLYManual042909.pdf
To find the information below; Use within the pdf search:  at least 6” above
Or use down arrow to P-8 & scroll down a-ways...

"If the oil furnace is used in connection with summer air conditioning the evaporator coil must be installed at least 6” above the oil furnace for proper airflow. Distances less than 6” will result in decreased airflow."
Make sure outlet supply takeoffs are NOT blocked by the coil. In all cases, refer to the manufacturers’ data for static pressure losses to ensure the total system static pressure does not exceed 0
.5” WC.
My Scan of My ThermoPride OL 11 Graphed Blower-Curve-Chart
Thermopride OL 11 Graph ipg image - Thank you Dave Staso, CA. for the better expandable image!
"After it loads Right click "Show Original Images" - Move cursor arrow over graph - Click + when 'over graph' for expanded image," then print on the highest quality setting.

Every manufacturer should furnish blower line curve charts with their units and put them on the Internet for service tech's to download and print. A blower curve graph chart, for discerning the variables of ol furnace belt drive blowers. 

Observe how easy it is to fall below the required CFM with a quarter horse blower belt drive motor that was standard with 112,000 Btuh output oil furnaces. Measuring the static pressure of the duct system & using an anemometer to check actual airflow is a must! The Thermo Pride OL 11 Oil furnace requires 1164-CFM of airflow to keep temp rise within 90-F.

That would require at least a 2.5-ton A-coil at 1125-CFM to get close to enough aiflow, a 2-Ton coil is only 900-CFM.

Dons 1.5 Ton Heil AC Data Chart Condenser is ejecting HALF the heat of its Nominal Rating; evap-coil way under heatloaded! The importance of a full heatload on E-Coil.

-------------------------

The North Country Oil furnace A/C or heat pump scenario:

Any good Tech should already know what I am going to illustrate here; this is for Homeowners & any who can use the least costly way to deal with this too common a problem in the cold North Country.

We are moving into the cooling season; however, any changes in equipment should consider how every component matches with optimal airflow efficiencies.

My lowest cost solution to the cold climate oversized Oil furnace with a small tonnage A/C evaporator coil which requires nearly half the airflow as heating:

I ran a check on my late brother’s home & the summer cooling heatload is about 14,000-BTUH.

The original scenario, had much less airflow than required for 1.5T cooling; its 2-T A-Coil wouldn’t flow 1150-cfm for heating

I did a lot of other figuring; 45,000-BTUH output should heat that small single story home.

However, with the 140,000-BTUH input, 112,000 output Oil furnace installed; the nozzle size can be dropped from one gal an hour (we’ll use 139,000-BTUH input) to .75 @100-psi, the BTUH drops to 103,500 input, this furnace tested at .74% efficiency; *103,000 = 76,590-BTUH.

Using a 90F heating temperature rise, which Thermo Pride can stand; (90*1.06 here) 76,590 / 95.4F is 803-cfm.

Therefore, the 2-Ton A-Coil will handle the CFM; mounted +6 inches above the furnace, it has the flow capacity to work okay in both heating & cooling modes.

With a third HP belt-drive motor, you could simply adjust the RPM down by turning the adjustable motor pulley out enough to get to 700 or 600-CFM for the 1.5-Ton A/C.

The other solution is to install a multiple speed direct drive motor with the fan relay energizing the cooling speed tap.

This rather common situation in cold climates seems not to be properly addressed my Techs, & the HO does not know why things don't work well.

We should all work to improve efficient use of high cost energy ... so America & everyone wins.
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Home & small business owners, here is a very low cost way to check an A/C or heat pump's cooling BTUH performance. Get a low cost Testo 605 Tester to get the Supply Air Wet Bulb temp & Return Air Wet Bulb temp so you can ballpark figure actual BTUH & EER performance:
Testo 605-H2 Fast Accurate Wet Bulb
Home & small business owners & everyone, very low cost anemometer to get airflow FPM Velocities at Supply Registers or Return Air Grilles, which you can convert to CFM:
http://www.amazon.com/Crosse-Technol.../dp/B0002WZRKE


Also, get a low-cost digital flat-headed pocket Thermometer to use flat on the piping; these test instruments will PAY big returns!
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Take the Supply Air & Return Air wet bulb temperatures & interpose them on the enthalpy chart linked below.
CFM X* 4.5 @sea-level X* change in enthalpy = BTUH (Ballpark) Operating Performance.
"U Must Right Click Link & open in New Tab," look-up wet bulb enthalpy figures on enthalpy chart," & figure enthalpy change times the result of the CFM X* the factor.
Wet Bulb Enthalpy Chart  Print chart
---------------------------------
Video  Best

:  Installing  &

Cooling Coil Best Practices NOT shown in this .


Install Best Practices Video:   needs to be at least +6" above an  or large Oil HT/EX will greatly restrict !
YouTube - How to  with Plastic Film-  Improvement  Do it RIGHT
-----------------------------------------------

Simple easy anyone can do ways to check the performance of your central air conditioner so, if needed, you can call an Energy Efficiency HVAC Technician

If U want me to run a ballpark analysis of how your system is performing in respect to its 'Nominal Rated Btuh' we need at least the following numbers:

Performance Data Collection – Best Time to collect data is Late afternoon around 4:30 pm, when attic is HOT; also when outdoor temps are around 85; 95; 105F or, anywhere in between.

 *All U need is a good thermometer (digital reading in tenths preferable) & and indoor Humidity Gauge

1) Helpful; Tonnage & SEER of Unit & outdoor condenser model number: __________________

2) TXV or, orifice metering device? _______. Only if U know…

3) Outdoor condenser’s discharge-air-temperature ______-F

Subtract Outdoor air temperature: _______

Outdoor Condenser Air-Temp-Split _______ 

4) Need the ‘Indoor’ percent of relative humidity - away from Supply-Air outlets ______

5) Indoor Return-Air Temperature ______

Subtract Indoor Supply-Air Temperature ______ -F

 Indoor temperature-split _______-F 

Need the above information for troubleshooting & performance analysis.

Example below:

A Goodman 2-Ton 13-SEER condenser, 800-cfm indoor airflow; 80-F indoor dry bulb & 50% relative humidity; Indoor temp-split 18 to 19-F.

@ 85-F outdoors; 103.9-F - 85-F outdoors or around an 18.9-F temp-split; 

@ Indoor 75-F & 50% RH condenser temp-split is only around 14.9-F.

In summer an all electric farm home TWO Half-Ton Window A/Cs & basement large dehumidifier:

June 30, 2012; Darrell’s meter; 62610 – 62140= used 470-KWh * .0985= $46.295
================================

Rules of Thumb for Duct Systems  - Hart&Cooley
DESIGN AND INSTALLATION OF RESIDENTIAL FLEXIBLE DUCTWORK SYSTEMS
http://www.dca.state.ga.us/development/constructioncodes/publications/1ONE.pdf

Look at the ducting, if it is not to code; make hard copies of this code & give it to whoever does the ducting work
Make sure they redo it right!
Never have flex duct interiors commercially cleaned, I just viewed Home Inspection photos showing the interior damaged & insulation plugging the duct.
Home Inspectors warn people because the duct cleaner's tell them it won't damage the ducts. Some HI's look into the boot areas for clues of problems...

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Rules of Thumb for Duct Systems  - Hart&Cooley

Identifying your registers/diffusers & their (Ak) sq.ft. area, so you can multiply the FPM Velocity times the Ak to get the (CFM) Cubic Feet per Minute airflow from that register.
Have or do a manual J heat-gain calc for each room. If a room calls for 3,000-BTUH; first divide 12,000-BTUH by the CFM PER TON you want to use.

I.E., Wet coil, 12,000/400=30-BTUH per each CFM; Wet coil 12,000/425=28.235294; 3000/28.235-= 106.25-CFM;  Dry coil, 12,000/450= 26.6666-BTUH; 3500 / 26.6666= 131.25-CFM
If register/diffuser has the same (Ak) free-airflow-area, as the duct run!

Room calls for 3,500-BTUH, using 450-cfm per/ton dry coil or 26.6666-BTUH per CFM= 131.25-CFM.
I.E., 6" rd duct .6*6=36*.7854=28.2744sq.ins/144=0.19635-sq.ft.; 131.25-cfm / 0.19635-sq.ft= or 668.4-fpm velocity.

Importance of figuring static pressure & Amp draw changes in respect to CFM air flow changes:

  • SP2 (Static Pressure new) = {CFM-new / CFM-old}2 *X old SP1
    SP2= 1.5-Ton {600-CFM / 475-CFM}2 = 1.26157895 or 1.595567867 * .50" old SP= .80"SP new; too high
     SP2= 4-Ton  {1600-CFM / 1350-CFM}= 1.85185 * 1.85185= 1.4046634 *.55" old SP= 0.80" new SP2; too high
    SP2= 5-Ton A/C {2000-CFM / 1650-CFM}2 = 1.21212 * 1.21212= 1.469237833 * old SP  .55" = 0.80" new SP;  too high.

    It is always better to add Supply Air (SA) branch runs & more Return Area (RA) area, plus" a lot more RA filter area."
    On Oil furnaces, ALWAYS RAISE the E-COIL,where possible, 6, 8 to 10" above the Oil furnace!

    Fan amp draw increases as to the cube of the cfm increase
  • Amp2 = Amp1 {cfm2/cfm1}3 cubed *x Amp1= Amp2
  •  SP2 = {rpm2/rpm 1}2 X SP1 = SP2

Required fan motor horsepower (HP) varies as to the cube of the rpm speed:

  • hp2 = {rpm2/rpm1}3 x hp1 = hp2

CFM Fan delivery varies directly as to the fan RPM speed:

  •    cfm2 = {rpm2/rpm1} X cfm1 = cfm2
Duct retro-work can solve the problem, increasing blower HP alone won't usually work well! A few calculations plus retro-work and presto, a matched airflow with your systems' heat absorbing coil capacities, delivering near its BTUH, EER, and SEER ratings at normal room temperature settings! (Most don't)

http://www.americanmetalproducts.com/lima/product_catalogs.html
Click on the categories to see the diffusers & Return-Air Grilles then find them on your downloaded pdf's engineering data.
Hart & Cooley: http://www.hartandcooley.com/grd/HC-100/residential/baseboard_registers/462.htm
Do a lot of Hart & Cooley engineering data searches, look at the registers & the Ak sq.ft. data to figure register's delivered CFM.
LOW AIRFLOW - this will help to open your eyes!

Required fan motor HP varies as to the cube of the rpm blower speed.

Also, at 700-rpm & .2" SP for heating my Thermo Pride OL 11 with its quarter Hp motor will deliver 1200-CFM;  add a cooling coil, & at .5 SP it will deliver only 400-CFM.

Keeping the total static pressure as low as possible and within mfg'ers ESP requirements for air conditioning is the first requirement in an efficient system design.

BTW, what is the average pressure drop across the new +90 high efficiency furnace condensers? That pressure drop should be published by all of the companies!
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The North Country Oil furnace A/C or heat pump scenario:

Here is just one scenario; the small one story home with a basement requires only 14,000-BTUH of cooling but it has a 112,000-BTUH Oil furnace with a belt-drive quarter HP blower motor.

Three things have to be done right; first, the evaporator coil has to be sized to flow at least 1250-cfm that requires a 3-ton coil.

Second, the evaporator coil has to be mounted at least 6” above the Oil furnace to eliminate an airflow restriction between it and the super large heat exchanger near the top of the furnace.

Third, the belt drive motor has to be replaced by a multi-speed direct-drive blower motor that will deliver the correct 1250-cfm for heating & 600 to 675-cfm airflow for cooling.

I have witnessed a 2-ton evaporator coil being installed directly on top of the Oil furnace & the quarter HP direct drive motor left in place.

Can you cite the horrendous problems this creates?

Think through what you’re doing & the consequences before doing it
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WARNING: on units with a Thermostatic Expansion Valve (TXV), you cannot use the suction pressure to check the charge; many appear to be doing this; it tells you nothing. Only after you have verified that all the coils are clean & the airflow is right-on, can you begin to check the system's charge using Subcooling method with a Superheat check. Always check the actual Delivered Airflow CFM before checking the charge, get it Right!

* There is a TXV system that has very low airflow, actually less than 200-cfm per-ton of cooling, they're only checking the suction pressure & saying the charge & everything is okay! * That system has a TXV & shows; 98-F condenser saturation temp & 97-F liquid line temp near E-Coil, a mere 1-F Subcooling, it's undercharged even with a mere 200-cfm per-ton cooling load! Unbelievable, but it's happening out there...
Use my Superheat Subcooling Charging page!

==========================
Air Conditioning Performance Diagnosis using listed (CT) Condensing Temperatures
Using Goodman 16-SEER "Expanded Performance Data"

  Find the correct (CT) Condensing Temperature with the following known mfg’ers data.

Outdoor Ambient Temp (OAT) 85-F; IDB 75-F; IWB 63-F or 50%-RH.
Listed pressure is 316-psig, or 99-F CT; that is 99-F -85-F is a 14-F SPLIT.

The delta T or temp-split should be within a 10-psig range or, +/- 2-F degrees; 97 or 101-F.

The mfg’ers Supply Outlet should be able to provide Contractors & Techs with those performance data charts. Goodman has their “Expanded Performance Data” on the Internet. BTUH = CFM X enthalpy difference from Chart X 4.5
  <-Click

Size for cooling; size the equipment and system based on 100% of the Total Cooling Load (both sensible and latent loads) at actual outdoor design conditions. Size the duct system properly & make certain that the proper airflow & optimal heatload is passing through the evaporator coil during most of the operating runtime. To Optimize Payback and lower operating costs always do as many things as you can to Reduce the heatgain-heatloss "BEFORE doing the manual J load calc & manual S for sizing the equipment."

To select the “proper size” heating, air conditioning, and duct system for a home, seven factors must be considered and all changes made prior to sizing equipment:

1. Improving Insulation Values and Reducing Infiltration, including e-windows, doors, etc.

2. Reducing Air leakage - air leakage accounts for between 25 percent and 50 percent of the energy used for heating and cooling in a typical older residence.

3. Solar orientation - and ways to reduce the radiant heatload should be considered.

4. The Internal BTU heat generation of appliances and people must be added.

5. Design conditions (typical outdoor and indoor weather conditions, humidity levels, etc.) A scientific calculation (manual J) called a Heat Loss/Heat Gain Calc, tabulates these factors into a load scenario for heating and cooling based on summer & winter outdoor design conditions for the climate where the home is located.

By comparing the heat loss/gain to manufacturer's equipment performance data, a properly sized heating and cooling system is selected. Use indoor design of 75-F dry bulb and 63-F wet bulb, around 50% Relative Humidity.

6. Proper & thorough ductwork testing and design Is Extremely Important for efficiency & BTUH performance - The evaporator coil needs to have an optimal heatload passing through it most of the time in order to approach achieving its Rated BTUH Capacities & its EER & SEER Ratings.

7. Study the diffuser data in respect to room CFM, the required throw & a diffuser Face Velocity of around 600-fpm, & a Terminal Velocity at the human occupant level area of 50 to 75-fpm. This is critical toward achieving an optimal human comfort zone.

What should you expect from the average heating and cooling contractor?

When a typical heating and cooling contractor quotes the efficiency of the equipment (SEER or AFUE) and leads you to believe the new equipment will automatically deliver that efficiency, think again. Typical installed equipment only operates at 55% to 70% of rated capacity.

It is important to understand that equipment ratings are only "the potential efficiency of that component of the system under perfect conditions." "Over half of the system's efficiency depends on the duct system and the field-installation." Check for Return Air drawing Hot Air from attic areas, etc.!

An A/C's system efficiency can often be increased by a skilled tech from 10% to 50%. The biggest benefit is the increase in comfort and lower utility bills!

The heat loss/heat gain calculates the amount of heat transfer by component, based on the surface area, and then tabulates the total transfer for all of the components.

Air leakage > air infiltration: Up to 50% of an average home's heat loss/heat gain is attributable to air leakage, air infiltration. Therefore, determining the proper leakage/air infiltration rate for a specific home is paramount. Design leakage/air infiltration rates are based on dwelling size and projected efficiency or actual measured performance.

Solar orientation, or the amount of window surface area and the direction a home faces can have tremendous impact on the cooling needs (heat gain). Similar houses with different solar orientation will have different cooling loads. Glass facing east/west has more heat gain than glass facing south or North.

The service techs should use a manual D to properly size the ductwork supply air mains and runs to outlet diffusers, as well as the “sizing of the return air ducting in relationship to the BTUH/CFM requirements of the various rooms.”

Qualified personnel must perform all installations and services. The duct system sizing and load sizing calculation should follow the design standards of Air Conditioning Contractors of America (ACCA) - Manuals D & J -or the American Society of Heating, Refrigeration & Air Conditioning Engineers, Inc. (ASHRAE) Fundamentals Volume (latest edition).
----------
When sizing ducts, the use of one value throughout will assure incorrect duct size for many branch runout duct segments. If 0.05 is used, nearly half of the runouts of the system will be oversized, resulting in those zones being too cold in summer, resulting in the remaining runouts furthermost from the air handler being undersized, creating zones that are too warm in summer.

The result is a human comfort design failure. The modified equal friction method of Manual D, "requires that the available static pressure from the fan be 'consumed' by the duct through its run from fan to outlet/inlet, with no shortage or excess at the end."

Pressure drop per 100 ft is not an input, it is a calculated intermediate value. A contractor who knows how to do the calculations to determine the available static pressure, and correctly allocate it to the supply runouts and return, is a rare tech.

 This page does not explain everything you need to know about proper duct sizing a system for optimal comfort, but provides some general guidelines and concepts.
======================================================
 
*You could ballpark the CFM using the static test & the air handler's graph. You could measure the CFM delivered to each room with a hood Alnor Balometer, it's usually the best instrument to use, but not cheap. Measuring the air velocity from diffuser's is a bit tricky because you should use the diffuser mfg'ers data which you should always have with you.

You can usually get the diffuser mfg'ers data, say its a 1.5-Ton system that already has 6"rd branch duct runs, to achieve enough CFM airflow, you need 700-FPM velocity in the ducts.
I would want to use a diffuser with a little more free open sq.ft area than the 6" duct  which area is 0.19635-sq.ft., say middle of the room in the ceiling;
Hart & Cooley 2-way curved blade 12x6 has Ak .235-sq.ft. Free-Air-Area delivering 140-CFM at 600-FPM - diffuser face velocity.

This would help lower the velocity of the duct
through the diffuser & reduce air noise.
Throw is 7.5-ft toward each wall. Terminal velocity at the occupant level is 75-FPM.

One duct yields 140CFM times 5 outlet runs yields 687-CFM *X's 30-BTUH per CFM = 20,616-BTUH, about right.
Whatever CFM you need for that room or area, divide the Sq.Ft.
free-air-area into the requires CFM to get the FPM velocity.

Say we're using 450-cfm/ton of airflow; 12,000-BTUH / 450= 26.6666-BTUH per CFM. You need 3600-BTUH for that room, 3600 / 26.666 that's 135-CFM / by .235-sq.ft. diffuser area is  only 574-fpm face velocity. 
Using 400-cfm per/ton / 12000-BTUH is 30-BTUH per CFM.

Taking the manifold gage head pressure & gage condensing temperature is very important data. Coupled with a condenser air discharge temp-reading, if the condenser gage pres/temp is too high compared to the TH reading, there may be non-condensibles in the system.

Also, there is a legitimate formula I use to determine the operating BTUH it is delivering at all the data taken. All the mfg'ers ought to list the condenser temp-split (it varies with EER & SEER) just like they list the indoor split, it is valuable trouble shooting info.

You can also use the condenser temp-split (it contains both Latent & sensible heat) combined with the indoor data to plot the indoor CFM. I was never good at math, but those equations have to balance, & they do work!
======================================
Quick Check for Sizing Units to enough Airflow
Home owners, actually, even on service calls where there are cooling problems the ductwork should have a quick Manual D performed.

Then take the ESP static pressure & compare to blower graph or chart, also take the FPM duct/diffuser velocity.

Have or do a manual J heat-gain calc for each room. If a room calls for 3,000-BTUH; first divide 12,000-BTUH by the CFM PER TON you want to use.
E.G., Wet coil, 12,000/400-cfm per/ton=30-BTUH per each CFM; Wet coil 12,000/425-cfm per/ton=28.235294; 3000/28.235-= 106.25-CFM.
E.G., 6" rd duct .6*6=36*.7854=
28.2744sq.ins/144=0.19635-sq.ft.;using 450-cfm per/ton dry coil: 131.25-cfm / 0.19635-sq.ft= or 668.4-fpm velocity.

Then do a quick estimate of airflow per equipment tonnage.

To find area of a round duct; Duct diam is 7"; 7"X7"= 49-sq.ins., X's .7854 = 38.04845-sq.ins divided/ by 144= 0.2672541-sq.ft. area X's FPM Velocity 600-FPM = 160.35246-CFM X30 = 4,810.5738 each 7" run X's 6 branch runs = 28,863-BTUH, or airflow for 2.4-ton.
(12,000-BTUH /400-cfm per-ton = 30-BTU per cfm ratio | / 450 = 26.666-BTUH per-cfm)

That would also be good for 2-ton; at 550-FPM velocity X's 0.2672541= 147-CFM X 30 = 4,410-BTUH each run X 6-runs = airflow for 26,460-BTUH.

*Never sell units requiring more airflow than the duct system will support! - Darrell udarrell


Actually, even on service calls where there are cooling problems the ductwork should have a quick Manual D performed.

Then take the ESP static pressure & compare to blower graph or chart, also take the FPM duct velocity.

Then do a quick estimate of airflow per equipment tonnage.

To find area of a round duct; Duct diam is 7"; 7"X7"= 49-sq.ins., X's .7854 = 38.04845-sq.ins divided/ by 144= 0.2672541-sq.ft. area X's FPM Velocity 550-FPM = 160.35246-CFM X30 = 4,810.5738 each 7" run X's 6 branch runs = 28,863-BTUH, or airflow for 2.4-ton. 

That would also be good for 2-ton; at 550-FPM velocity X's 0.2672541= 147-CFM X 30 = 4,410-BTUH each run X 6-runs = airflow for 26,460-BTUH
(12,000-BTUH /400-cfm per-ton = 30-BTU per cfm ratio | / 450 = 26.666-BTUH per-cfm)

Don't have supply air diffuser engineering data: free air area of Hart & Cooley, one, 2 & 3-way diffusers is about 50% of the sq.ft. area of the diffuser's listed size. Multiply that figure by FPM velocity to get the CFM.  Also, search, Lima & J&J Register for their (Ak) numbers.

 
Google search Hart & Cooley, also this pdf might help you select the right diffuser for the particular application, & list (Ak) free sq.ft., area of the diffusers:
http://www.rileysales.com/hottips/resizingreganddiffuser.pdf


Recommended Return-Air main velocities should be 600-fpm or less, on Branch Return Air ducts try for 550-fpm or less velocities.
Keep air velocities through the RA Filter(s) as low as possible.

RETURN AIR FILTER RACKS
Manual D, recommended clean filter velocity is 300-fpm, lower yet  is better.  See the math below.

 Velocities higher than 500 fpm will decrease filter performance. Increase flow resistance, and possibly
blow off collections of dirt. Measure Velocity 1” from RA grille face.

Average Free Air area of most Return Air grilles about .90%; Clean Return Air Filter free-air-area is around .50% this will vary; I use .45% for both.

Therefore, measuring the open area of the grille sq.ins. X's .45% initial 900-sq.ins= 405-sq.ins.,
/ 144=2.8125-SF *X 300-FPM Vel = only 843.75-CFM of airflow; enough for a 2-Ton system.

. 
Never sell units requiring more airflow than the duct system & filter area will support! - Darrell Udelhoven udarrell

---------------------------------------------------------------
An affordable test instrument you need!
All I had was the Sling Psychrometer & spinning it was a bit time consuming, but I used it religiously, it is information you need. 

The Testo 605-H2 Humidity Stick (wet bulb), displays relative humidity, air temperature and wet bulb temperature.

It is very affordable & because of its potential to help deliver tons of other data everyone should have one!

For more information on it:
http://www.amazon.com/Testo-605-H2-H.../dp/B000774B6A

The other test data you need is the system's CFM airflow through the evaporator coil, then with software I have you can peg the BTUH the operating unit is delivering under those conditions.
Add to that a low cost Magnehelic gauge to read static pressures to compare with mfg'ers blower performance charts; plus a velocity meter & you have a ballparked CFM to plug into for the BTUH.


We could easily provide a detailed psychrometric print out of exactly what the operating system is delivering including condensate lbs/hr, & actual sensible & latent cooling BTUH & Ratio, every data detail imaginable.

Think about what that would mean to you & those you serve. - Darrell

============================
Determining which metering device the system has without physically looking

If you do not absolutely know whether the metering device is a TXV, or a fixed orifice device or cap tube. 

Hook up your manifold gauges, block off considerable condenser air intake for a short time.
If the suction pressure starts rising, you have a piston, or a cap tube.
If only the high side goes up, you have a TXV.
Double check using Superheat, if Superheat stays relatively stable when the pressures change it's a TXV.
Have things with you in your van or truck to block-off the entering condenser air for a short time.
Check every time you are not certain what metering device it has.
There will be a lot of guessing in the future.

Do this procedure on known metering devices to observe the difference.
Report back to me how well it works for you.

In some situations, that could save you from cutting a hole in the plenum.
--------------------------------------------------------------------------------------------------

Supply Air (SA) and Return Air (RA) -- near the ceiling or near the floor
For cooling both SA and RA work better near an 8 foot high ceiling. The SA diffusers should distribute the air near the ceiling to the walls on all sides of each of the rooms.
Whether a single return system, or a multiple return system is used, there must be a low resistance path between every room and the nearest return air opening. This can be done by using wall transfer grilles, door grilles, or jump ducts.


To quickly aid you in evaluating existing duct systems, review the chart below. To insure the necessary air handling capacity of a duct system, each of the system's components (trunk lines, takeoffs, runs, diffusers, registers, and grill free areas) must be properly sized and matched together. A 12x8 duct with a 350-CFM capacity, for example, WILL NOT flow 350-CFM if the boot & diffuser(s) combo can only flow a total of 200-CFM within specs.

This Hart & Cooley pdf might help you select the right diffuser for the particular application:
http://www.rileysales.com/hottips/resizingreganddiffuser.pdf

The boot size & register size is determined by the throw, spread, drop, Terminal Velocity of 50 to 75-fpm at the occupant level, & noise class according to the CFM that must be delivered to the room. Those specifications are located in the technical engineering pages that the diffuser mfg'er has available to the dealer distributors. 

When sizing the return air duct system, the air handling capacity MUST BE EQUAL TO the SUPPLY SYSTEM at a minimum, I would oversize the return ductwork. It is recommended that contractors follow design parameters established by ACCA or ASHRAE on the return air duct systems.

If at all possible, use insulated metal ductwork.  For Heat pumps, Figure 450-
CFM per BTUH ton CFM | Round Duct | Square Inches | Rectangular Ducts | SA use 0.06" Friction Rate (FR) per 100 foot, 0.05" FR for Return  Air.


FIGURING ROOM CFM - DUCT SIZES

Using manual J heat-gain calculations for each room for cooling, then add up all of the rooms for the entire house.

You must know & record the operating feet per minute (FPM) velocity & the CFM to each room & the Total CFM airflow! Every tech should be using an anemometer to check operating airflow velocities in FPM & then figure the CFM airflow's.
Another quick method: The heat gain and Btu/hr of cooling is done for each room.
At 400-CFM per/ton of cooling, 12,000-BTUH / 400-cfm = 30-BTUH for each (CFM) Cubic Foot per Minute of Airflow.
At 460-CFM per/ton cooling use 12,000 / 450-cfm = 26-BTUH per each CFM, I would use 460-cfm per-ton for airflow & duct sizing; 3000-btuh / 26= 115-CFM at 600-fpm velocity with a 6" duct run.

You must know & record the operating feet per minute (FPM) velocity & the CFM to each room & the Total CFM airflow! Every tech should be using an anemometer to check operating airflow velocities in FPM & then figure the CFM airflow's.

Another quick method: The heat gain and Btu/hr of cooling is done for each room.
At 460-CFM per/ton cooling use 12,000 / 460-cfm = 26-BTUH per each CFM, for duct sizing.

Then Select Supply duct size by CFM, velocity, & optimal Supply Air *(FR) Friction Rate.

Using 460-CFM per ton; a Room requires 3600-Btu/hr divided / by 26 equals 138-CFM, or around a 7" dia. RD metal duct.
You need-> Five duct runs for 1.5-ton unit, 18,000-BTUH: (If were Equal room loads) 18000 / 5-runs= 3600-BTUH / 26 = 138-CFM each 7" duct velocity 500-fpm Velocity
20' branch runs 500-fpm velocity at a Friction Rate 0.03" per 20'.

Formula for finding CFM Airflow
If you can measure the air velocity coming from a duct, here is a rough ballpark formula to get the CFM:
CFM = (velocity in (FPM) Feet per Minute times the square footage of the duct area)
I.E., 16" Rd duct 201-sq.ins. X's 0.00694 = 1.39494-sq.ft. X's Velocity of 800-fpm = 1116-CFM
Times 1000-FPM = 1395-CFM. Branch ducts: 7" Rd duct 38.48-sq. ins. X's 0.00694 = 0.2670512-sq.ft. X's 500-fpm=133.5-CFM
Example, times a velocity of 600-FPM X's 0.00694 = 160-CFM, the velocity is a big CFM & BTUH number changer for rooms.


It is better to use a ductulator to enable the use of the appropriate Velocity Friction Rate balances to achieve the correct CFM on each Branch Run, etc.


This chart is in accordance with the tonnage of the unit.
Residential metal Duct Design varies from as low as .02" on Returns, to -
Supply Trunk runs down to 0.05" Friction Rate pressure drop per 100 feet of duct.

Refrain from using Flex duct, if unavoidable, use .03 to .05 pressure drop or lower per 100 feet of duct run.
A 3.5-Ton main run at 450-CFM Per Cooling Ton would require an 20" rd main trunk run, which will also work for heat pumps.

1575-CFM | 20" rd duct | Gross sizing of Return Air (RA) filter grilles: 200 sq. ins. Per Ton of cooling.

A 5-ton system should have two 500 sq. in. Return Air Filter Grilles. (Or,  (two) 25" x 20" Return Air filter grilles for 5-ton.)
 
This is to try to reduce the air velocity through a clean filter to 300-FPM and to reduce the resultant pressure drops as the filter loads. The free air area of a filter should be stated on the edge of the filter by the mfg'er.

It is very important to size each duct to the CFM and velocity needed for the room served in accordance with the manual J load and manual D duct design. Dampers’ on too large a duct, if dampered too much, would result in too much velocity loss.

Once you know the manual J loads, number of duct-runs and the Velocities, Friction Rates, & CFMs for each room, you can use the register/diffuser data to get required throws, etc. (i.e., Hart Cooley from your supplier).

Example: One-Way - Adjustable 10x6 diffuser; select a duct size that provides 80-CFM @ 600-fpm, which will provide an 8.5-foot throw. Hart & Cooley lists a Pressure Loss through the diffuser at .022” of an inch.

Consider the register/diffusers you are going to use and the various CFMs’ & Throws’ you need according to your design layout. – Darrell 

DUCT SIZING CHARTS Residential Main Trunk Runs for Approximately 450-CFM Per Ton - First USE Manual D for sizing!
Residential Supply Air - used 800-FPM as MAX for Main Runs - On chart, SA: Supply Air; RA: Return Air

1.5 ton 700-CFM
13"metal Main133-sq."SA 760-fpm FR .07 | RA 16" 201" 500-CFM  FR 0.01" (FR. 25' run)
1.5 ton 750-CFM
14" Branch 154-sq."  702-fpm FR .05 | RA  16" 537-CFM per ton SA/RA floor level
2-ton 900-CFM
14-SA Rd 154-sq." 854-fpm | 18"-RA 254 @ 510-fpm
2.5-ton 1125-cfm
16" metal  Rd 201-sq"  806-fpm | RA 20" RA 516-fpm 
3-ton 1350-cfm
18" metal 254-sq" 764-fpm | RA 22"  512-FPM
3.5-ton 1575-cfm
20"metal 314-sq"  | RA 22" Rd 314-sq" 531-FPM 
4-ton 1800-cfm
20"-SA 314-sq" 825-fpm | RA 24" Rd 380-sq" 573-fpm
5-ton 2000-cfm
22" SA 380-sq" 758-fpm  | RA 24" Rd 452-sq" 637-fpm

Tonnage ChartsFormula for finding CFM Airflow from Velocity in FPM above for Main Run Sizing, check chart below
If you can measure the air velocity coming from a known size duct or open area of a SA register, here is a rough ballpark formula to get the CFM:

450-cfm per ton | Maximum 900-fpm Trunk Supply Air (SA)
Runouts 500 to 600-fpm, 500-fpm or less on Returns |
Return Air 350 to 600-fpm Lower is better - use large ducts
The filter rack area sized for free-air-area to achieve an initial 300-FPM velocity through the filter
Friction Rates will be very low!
Main Trunks 0.03 to 0.1" Supply Air (SA) Runs.
Figuring duct size - cfm from required BTUH of each room. Using 450-cfm per 12,000-BTUH (one ton) 12,000 /  450 = 26.66-BTUH per CFM

A room  requiring 4,000-BTUH / 26.66 = 150-cfm | Chart 150-cfm = 7" round metal duct or 38.48-Sq.In. Square duct. Using Metal Duct!
I would use a 7" duct, or a 38.48-sq.in. duct. Using 425-cfm per ton 12,000-BTUH 4,000-BTUH is a third of 12,000-BTUH.
Therefore, 4,000-BTUH room requirement, using 450-cfm per ton (airflow 1/3 of a  ton) X's .3333 =
150-cfm or  7" duct | 25' with (2) 90's, Vel. 562-FPM  Friction Rate (FR)  0.04"



CFM = (velocity in (FPM) Feet per Minute times the Square Footage of the duct area). To convert sq.ins. multiply by 0.00694 for sq.ft., or divide sq.ins. by 144.

Converting square duct
inches to round duct size, Figuring the Square Inches of Round Ducts, an 8" x 8" duct = 64-sq.ins. x .7854 = 50.26 sq. ins. You round off to 50 sq. ins. for an 8" duct.  Or, simply getting the square inches of round ducts: a 7" duct; 7" x 7" = 49 x .7854 = 38.48-sq.ins. or divide / by 144 = .2672222-sq.ft. X's a velocity of 500-fpm = 133.6-cubic feet per minute delivered to the room; 133.6-cfm x 30 = 4,008-BTUH.


Sized for in the chart below - BTU/hr per CFM figures "are figured for heatpumps at 450-CFM per ton of cooling."
Use 800 to 900-FPM MAINS' VEL. Use an optimum of 500-FPM VEL for Supply Branch Runs | Air speed Face of Return. 

Air Filter Rack Sizing
ACCA Manual D specifies on Return-Air Filter grilles a maximum of 300-FPM velocity:
Recommended Main Supply-Air velocities for rigid duct should be 700-fpm & a Max of 900-fpm, for flex duct 600-fpm.
Recommended Branch Supply-Air velocities rigid & flex 600-fpm.

Recommended Return-Air main duct velocities should be 600-fpm or less, on Branch Return Air ducts try for
550-fpm or less velocities.
Keep air velocities through the RA Filter(s) as low as possible.

HVAC-TALK
Andythedrew 10/08/09 | Quote:
Is a 24x30 filter grille large enough for a 3.5 ton system?
Yes & No...
RETURN AIR FILTER RACKS
A filter grille is to be sized not to exceed Manual D's 300-fpm maximum velocity.
Use the tonnage's CFM /divided by 300-FPM Vel. = sq.ft. of free-air-area of filter & grille |
CFM /divided by
filter grille's sq.ft. free-air-area = FPM velocity.

You really can't have too much filter grille area; more is always better because they are always loading.
ACCA Manual D specifies on Return-Air Filter grilles a maximum of 300-FPM velocity.

Velocities higher than 500 fpm will decrease filter performance. Increase flow resistance, and possibly blow off collections of dirt. Measure Velocity 1” from RA grille face.

Average Free Air Area of most Return Air measured grille portion is about .95%; Clean Return Air Filter free-air-area is around .55%, this will vary; I use .50% for both. You can put in real deep pleated filter grilles; always have a deep enough box to the RA duct so the [U]filter area[/U] is not reduced to the entry diameter of the RA duct.


The filter mfg'ers ought to be required to list the free-air-area of their filters, & then state on the packaging or on the filter, the limit of CFM to stay within 300-fpm velocity through their clean filter.

Then how much free-air-area does that filter design have?
That depends on the type of filter(s) used.


Most 3.5 to 5-Ton systems require two filter racks exterior of the airhandler to achieve a low enough air velocity through those filters. Most 4 & 5-Ton systems nearly always have too much air velocity through initial clean filters, let alone when they begin loading.


Average Free Air area of most Return Air grilles may be about 90%.


Most 4 & 5-Ton systems require two filter racks
exterior of the airhandler to achieve a low enough air velocity through those filters. Most 4 & 5-Ton systems nearly always have too much air velocity through initial clean filters, let alone when they begin loading.

For a heat pump system, I would go for 4-ton sizing on the Return-Air Filter Grilles for your 3.5-Ton condenser & 4-Ton indoor cool.
 
For Example on a 4-Ton A/C or Heat Pump:
Let's look at two,  Return Air rack/grilles 625-sq.ins., each for 1250-sq.ins *X .75% = free-air-area of 937.5-sq.ins., X's .75% for the filter = 703-sq.ins., / 144 is 4.88-sq.ft., 
free-air-area; then 1600-cfm / 4.88-sq.ft. is 328-fpm velocity with a clean filter in the rack. 

The filter will reduce the sq.ft. free-air-area, thus increasing the fpm velocity, as it loads.
 


*All filter mfg'ers should print the free air area of the clean filter on the edge of the filter (we need that data) along with the pressure drop data.
Velocity in FPM =  Known designed CFM to room divided / by Sq. feet of duct area.
 I.E., 8" duct 8x8 = 64 x .7854 = 50.26-sq. In. area / 144 = 0.3490666-sq.feet | designed CFM to room is 173-CFM /  .3490666 = Velocity of 501-FPM, you can use a ductulator to get the actual Friction Rates (FR). See using the diffuser's Ak, below.

Formula for finding CFM Airflow and/or Velocity in FPM & BTUH

If you can accurately measure the air velocity coming from a duct, here is a rough ballpark formula to get the CFM:
CFM =
 (velocity in (FPM) Feet per Minute times the free-air-area (Ak) square footage of the supply-air diffuser.)
I.E., diffuser Ak is .225-sq.ft., times say 600-FPM velocity = 135-CFM
Also, (12,000-BTUH / 460-cfm per-ton ratio = 26-BTU per cfm ratio, for duct sizing)

 
Remember:

When sizing ducts, the use of one Fiction Rate value throughout will usually guarantee incorrect duct size, velocities & CFMs for some duct run segments. If Supply Side is 0.05" per 100 ft of duct run, or less is used, some runouts of the system may be oversized, creating zones that are too cold in summer. Usually the furthest from the air handler will be undersized creating zones that are too warm in summer. Install dampers in all Supply Air ducts for some balancing.

That is an incorrect design. The modified equal friction method of Manual D requires that the Available Static Pressure (ASP) from the fan be "consumed" by the duct through its run from fan to outlet/inlet, with no shortage or excess at the end. Also, pressure drop per 100 ft is not an input--it is a calculated intermediate value.

A contractor or Tech who knows how to do the proper calculations to determine the available static pressure - ASP and correctly allocate it to supply and return, is a very rare Tech indeed. First, select the CFM & velocities you want, that may result in small Friction Rate variations on the various Branch Runs & run lengths.

Always use "Manual D" for proper FRs & duct sizing for required CFMs to each room.
I used figures & formulas below for the table, & wanted 450-Btuh dry coil per ton airflow

Converting square duct inches to round duct size, i.e., an 8" x 8" duct = 64  -sq.ins. x .7854 = 50.26 sq. ins. You round off to 50 sq. ins. for an 8" duct.
Round duct diameter to Sq. Ins., duct diameter 6"x6" = 36 X's .7854 =
28.27-sq. ins.
CFM = (velocity in (FPM) Feet per Minute times the square footage of the duct area)
Quick method: The heat gain and required Btu/hr of cooling is done for each room.
Cubic Foot per Minute (CFM) of Airflow times 30-Btu/hr will ballpark the Btu/hr delivered to each room.
 
Duct Sizing Chart Residential some Branch Runs some Main Runs - for Approximately 425 to 450-CFM Wet Coil Per Ton on Main Runs. Always use ACCA Manual D to select duct sizing.
Residential Supply Air - used 800-FPM as MAX for Main Runs - 600-FPM MAX for Branch Runs - SA: Supply Air; RA: Return Air
BTUH
CFM
Rd. DIA. | Sq.Ins.
Sq.Ins"
Vel / FPM

1140
45
4" Sm. Rm
12.5
516





2100
70
5" Bd. Rm
19.6
514
 




2250
75
5"
19.6
552





3300
110
6"
28.27
550

14x2
7x4


3676
130
6"
28.27
662
7.5-mph
5-runs>
650-CFM
+18,000-BTUH


4500
150
7" Br
38.48
562
6.38-mph+2-Ton
10x4
8x6
7x6

5400
180
8" Br
50.26
516

7x7
10x6 8x7

6666
 222
9" Br
64
505

8x8
10x7
12x6

9812
327
10" Br
78.5
600
6.8-mph
14x6 12x8
16x5

18000
600
12" SA-Main
RA 12"
113 RA
0.7854
SA/RA
764-fpm
RA 10X12



18000
700
14"Metal SA/RA
SA/RA107
SA/RA 654
RA 12x12

24X8
16X10

24000
900
14" Metal SA RA-16" 201 RA
RA 645-fpm
RA 14x14
18x10
20x8
14x12

32000 1125
16"SA/RA 20"314
201SA RA 20"/516 RA 10x18
20x16 24X14


36000
1350
18"SA | RA 22" 380"
254 SA
RA 22" /512 24X16
20X20
18x22


42000
1400 20" SA/RA 22"
380-RA
RA 597
SA 642-fpm
18x22 16x24


48000
1600
20" SA/RA 22"
314-SA
SA-734-fpm
RA-606-fpm
16X20
24X14



60000
2000
CFM
22" SA 380-sq.ins
RA 24"
380-SA
452-RA
SA-0.04"FR
SA-758-fpm
RA
-637-fpm
RA 14x32
16x30
22x22
24X20

58000
1750
22"SA/RA 2.6368-sf
SA/RA
663-fpm
14X30
12X32




Solving for Available Static Pressure (ASP) - When Designing or Redesigning Duct Systems, Finding TEL, FR:
Total Equivalent Length (TEL)  Find the Total Return length, then find the longest Supply Equivalent Length (EL) by finding the longest measuring duct length, number of EL in the turning elbows, trunk take-offs, boots, etc.

Once you have all the correct Device Pressure Losses (DPLs) on the longest Supply Air run, evaporator coil, diffuser, etc.
Use the manufacturer's nameplate pressure (IWC) or .5" ESP and subtract all airstream device pressure losses in the longest TEL duct run (supply diffuser, damper, wet coil, etc. all available in manual D) from that given value. That will leave the "Available Static Pressure" - ASP for duct & blower design purposes.


You can figure the Total Equivalent Length (TEL) by using the Manual D length additives for the various fittings, then use your Duct Designer ductulator to properly size the duct system to meet the required CFM, velocities, FR as required in respect to the blower's Nameplate ESP, normally, 0.5" and its performance graph in relationship the remaining (ASP) Available Static Pressure.

There are charts available to determine what the total pressure drop will be then when you figure the "Total Equivalent Length" run of the longest Supply duct runs;
ALL lengths of duct and ALL fittings trunk duct take-offs, etc., to get the Effective Length (EL) additive to that duct run for the 'Total Effective or (TEL) Total Equivalent Length.'

Subtract the total Device Pressure Losses (DPL) from the AH equipment's "Available Static Pressure," usually .5” ESP because most furnaces are designed for .5" ESP to achieve the desired high speed CFM, if needed, you can always use a lower blower speed.

Then get a total equivalent length of your ductwork most ductulators have this on the back of them.  Friction Rate = Available Static Pressure times X’s 100; divided by the TEL, that is the friction rate per 100 ft of SA &/or RA ducting.

TEL ASP FR Chart Graph  Loads slow using dailup - Save both the pdf to a quick access PC folder for review

Designing or Redesigning Duct Systems Chart  Print

Variable Speed Motors and Static Pressure

It will deliver the required CFM with some blowers, but at a higher operating cost.
If there are any ductwork air leaks, it will throw everything off.

Nearly all duct systems have a percentage of air leaks.
Check for & minimize air leaks.
Blower wheels, evaporator coils, etc., everything has to be clean.

Get copies of the ACCA Worksheet; below is my math involved with the linked Graph:
On older furnaces, the .45-Device Pressure Loss (DPL) should be subtracted from a furnace Nameplate Max ESP .50-ESP, leaving only .05-ASP (Available Static Pressure).
According to the graph, (using a .45-DPL), ASP only .05 X 100 = 5 / by 330 = .015 Friction Rate, way too low & off the graph resulting in Inadequate Airflow!

It would need a much shorter TEL or less DPL's to meet design functionality!
Air Turning vanes in 90-ELLs greatly reduce the TEL.
Other changes could also help reduce the TEL.

First find 330-TEL graph, then look at the ASP at the bottom the the FR shown.
Also, a .06-FR is the lowest Friction Rate shown on that graph; though many use .05-FR on the Return Side.
Once the ESP has been determined, look at the fan curve for that particular blower and determine the CFM from that chart.

Looking at the product data chart, what temp-rise does the mfg'er recommend?
Measure the temp rise & see what you get.

Unless the proper CFM heatload goes through the evaporator coil it is nearly impossible to achieve an accurate & proper refrigerant charge, and BTU/HR along with efficiency will be way below Ratings! 
Take the static pressure measurements on both the Return and Supply Plenums of the furnace (with filter(s) in place.  

Drill two holes large enough to insert the static pressure tip, one on the supply side and one on the return.  Pressure measurements are then taken at each location.  The measurement on the return side will be negative with a positive reading on the supply but you disregard the positive/negative and just add the two numbers together.

When using two tubes (neg. & Pos.) on a modern gauge you will read what the gauge indicates!

Once the ESP has been determined, look at the fan curve for that particular blower and determine the CFM from that chart.

If the air flow is not per manufacturers' recommendations, it is near impossible to get the refrigerant charge correct.

EER
7 EER or less
8 EER
9 EER
10 EER
12 EER
13 EER
'Max' condenser air temp 'delta-T'
30
25
24
+23
+21
ave. less
Max temp drop 'across' E-Coil
20
22
24
26
ave. more
ave. more
'Max' SA/Return Entering Air 'Delta-T'
33
30
28
26
23
19

The Supply Air & the Entering Return Air delta-T, - tends towards less & less as the EER goes higher,
therefore, dehumidification could become more difficult at the highest EER levels. The EER & SEER levels widen, as SEER sky rockets.

Optimizing the "Evaporator HeatLoad" will Optimize the Condenser BTUH HeatLoad Output from your Home

Most evaporator coils are under-loaded when operating at the normal room temp setting!

The airflow should be adjusted to fully load the evaporator coil at the normal room temperature setting! This airflow adjustment will optimize your air conditioner's BTUH and SEER performance. Most air conditioner's have an underloaded evaporator coil at the room temp thermostat setting, where the vast majority of its run time will take place! In 8 foot ceilings, Return Air (RA) should always come from the warmer ceiling air areas.

On TXV metered systems the Subcooling should be within +/- 2-F of the mfg’ers installation instructions.

For Room Return Air balancing, i.e., -.01" IWC = approximately -2.48 Pascals, which is a more precise easier incremental scale to read.  One inch water column (IWC) equals, rounded to > 250 pascals; 0.5" IWC is about 125 pascals; 0.25" WC = 62.5 pascals; 0.125 = 31.25 pa.; 1 / 250 pascals =0.0040322 *X's  -2.50 pascals = -0.01003657696655" IWC or make it  - 0.01" IWC for low Return Air room pressure differentials; - use pascals.
==========================
Air Conditioning Performance Diagnosis using listed (CT) Condensing Temperatures

Using Goodman 16-SEER "Expanded Performance Data"

What is the correct (CT) Condensing Temperature with the following known mfg’ers data?

Outdoor Ambient Temp (OAT) 85-F; IDB 75-F; IWB 63-F or 50%-RH.
Listed pressure is 316-psig, or 99-F CT; that is 99-F -85-F is a 14-F SPLIT.

The delta T or temp-split should be within a 10-psig range or, +/- 2-F degrees; 97 or 101-F.

The mfg’ers Supply Outlet should be able to provide Contractors & Techs with those performance data charts. Goodman has their “Expanded Performance Data” on the Internet.

======================================================

My Scan of My ThermoPride OL 11 Graphed Blower-Curve-Chart
Thermopride OL 11 Graph ipg image - Thank you Dave Staso, CA. for the better expandable image!
"After it loads Right click "Show Original Images" - Move cursor arrow over graph - Click + when 'over graph' for expanded image," then print on the highest quality setting.


MOLO Plumbing & Heating sets the A-Coil at least 6" above a Thermo Pride OL 11 Oil Furnace. They know the importance of unrestricted airflow through the evaporator coil! http://www.molocompanies.com/plumbingandheating/index.html

Every manufacturer should furnish blower curve charts with their units and also put them on the Internet for service tech's to download and print. Also, air conditioning codes should be updated in respect to proper sizing of the duct work which must include all the pressure inducing factors when sizing the supply and return ducts. Also, illustrate best furnace to evaporator coil transitions, especially on oil furnaces!

The evaporator must be mounted 6 inches above this model oil furnace to achieve proper airflow!

Observe how easy it is to fall below the required CFM with a quarter horse blower belt drive motor that was standard with 112,000 btuh output oil furnaces. Measuring the static pressure of the duct system & using a vane anemometer to check atual airflow is a must!

DUCTWORK BASICS - Solving the Mysteries of ESP - External Static Pressure:
If you leave out the area up to & including the A-Coil where does that leave you? The area to the coil & including the coil can represent major Velocity -FPM losses & huge Static Pressure problems in Oil furnace applications. If there are any existing heating or cooling airflow problems, you can & should also measure & record each branch run static pressure, & velocity, then use the formula, CFM = (velocity in (FPM) Feet per Minute times the square footage of the duct area)
I.E., 16" Rd duct 201-sq.ins. / 144 = 1.3958333-sq.ft. X's Velocity of 800-fpm = 1116-CFM
IF Times 1000-FPM = 1395-CFM. Branch ducts: 7" Rd duct 38.48-sq. ins. = 0.2672222-sq.ft. X's 500-fpm=133-cfm
Deliver the exact CFMs to & through each diffuser that the application calls for!
Always look at the amount of CFM the diffuser's will actually pass at a specific velocity!
 DTI Corp
Air Infiltration Sources Up-to 50% of Load

DTI Corp Air Infiltration

Measuring Low Airflow

I normally would measure the airflow with a flow hood, also called a capture hood. You should normally have around

400 CFM (Cubic Feet per Minute) per ton of cooling. Half of the systems I measure have [a mere] 200 CFM per ton, OR LESS. This will be aggravated by a dirty air filter, Some Restrictive high efficiency air filter's or grilles closed in rooms that you are not using. Normally, do not turn the thermostat down below 70  [74 76 -better] degrees. says A/C Tech guru, 'Stretch'

First, before doing anything else check the sizing, and thoroughly seal and properly insulate all the ductwork!

DUCTWORK BASICS
In the linked pdf above: from pages 8 through 11 do NOT use those rules of thumb for sizing equipment & airflow to rooms! Use Manual J for heat-gain/heat-loss for each room & thus the total. Use the Manual S for heating & A/C equipment sizing! Then figure the airflow & ductwork sizing required for each room according to the airflow requirement for the cooling load, or Heat Pump load using Manual D.

Ductwork Retrofitting - An Excellent Economic Opportunity - Don't Miss IT

"More than 80% of the duct systems in residential and light commercial applications 'do not' work as designed." Do your service agreements include the duct system? If not, this is an important & significant business opportunity that you are missing!

Your best access into the duct renovation market is to include the duct system in your service agreements. What this includes is having the service tech measure static pressure on each service visit. Remember, this takes five minutes or less. If pressures are very high, or very low, send out a tech competent salesperson with a flow-hood and a manometer to identify the problem, and propose a bid to do the necessary ductwork fix.

One reason we have service agreements is to gain additional income from repairs, "so start repairing the real problem with the system," and not just the equipment. In most areas of the country there is very little competition for quality duct renovation and air balancing.

Prescribing HVAC repairs without competition from other contractors in a way that will greatly improve performance and efficiency, will delight your customers - that's our definition of opportunity.

Below is an outstanding PDF "Basic AC Overview - Specifications VS. Reality"
by John Proctor, P.E., Proctor Engineering Group, LTD:

HVAC TECH PERFORMANCE RATINGS 

"AC Specs Vs Reality" PDF - It's Worth Your Time
--------------------------------------------------------

EFFICIENT INDOOR COMFORT  - An EXCELLENT SITE  for You
FREE HVAC Resources for Professionals
===================
Quotes from linked PDF:
"Proper sizing, installation and maintenance of HVAC equipment are major
factors in operating efficiency. In fact, the potential energy savings from a quality installation are greater than those gained from the installation of high efficiency equipment.

Proper sizing and installation can result in energy savings of up to 35 percent for air conditioners and 16 percent or more for furnaces. Moreover, energy-efficient installation and proper maintenance practices also provide substantial non-energy benefits, such as greater comfort, lower maintenance cost and longer equipment life." Specification_of_Efficient_Installation1-36.pdf

==============
Always do Blower Door Test for air infiltration rates with the central air blower off & on, as infiltration could be a lot higher with blower on!

Home Energy Magazine Online September/October 1993

Raising Standards and Savings
New Group Hunts Bad Ducts

Does 40 billion kWh sound like a lot of energy? How about 4 billion therms? Researchers believe that's how much electrical and gas energy this country "could save by fixing inefficient ducts using current techniques." "Refining those techniques could reap savings of 90 billion kWh" plus 9 billion therms! Peak loads would be reduced too. To pursue these tremendous savings, national, state, and utility research laboratories, the U.S. Department of Energy, utilities, and energy service companies are collaborating. Their consortium is called "Residential Energy Efficient Distribution Systems," or REEDS.

These techniques, along with reducing air infiltration & heatgain/heatloss calcs, ought to be taught in all our schools as part of the Science, physics & math curricula. Up to half the heatgain/heatloss can be due to a high rates of air infiltration & heating mode ex-filtration heat loss!
ASHRAE standard 62-1989 is 0.35 ACH (Air changes per Hour) or 3-hours for a total interior air INFILTRATION Rate change
=============================================================
Darrell Udelhoven |  udarrell.com 

Gurgling sounds at TEV: Low evaporator heat-loads lead to reduced liquid line mass and increased evaporator mass could be due to airflow problems. Eliminate low evaporator heat-loads before looking into adjusting the refrigerant charge.
Gurgling and pulsation noises at the expansion device can be caused by low charge, and/or non-condensibles and moisture in the system. Unbalanced airflow through the various distributor circuits of the evaporator coil will cause the TEV to close down refrigerant flow starving the coil. Piston-flow-rators will make it impossible to properly charge the system and cooling will be greatly compromised unless you eliminate the cause!


On every Rheem condenser cover it lists "non-condensibles and or moisture" as causes for a gurgling or pulsating noise at the expansion device. The entire evaporator circuits, may not become active for various reasons, - "the entire coil must become fully active for efficient performance."

The purpose of these recommendations is to provide liquid refrigerant at the expansion device and provide efficient operation. Hopefully, this will aid your research.  If I can be of additional assistance, contact me.
-----------------------------------------------------------

Evacuation Procedures
Too many do not properly purge & evacuate "contaminated" central air conditioning systems.
First, the piping should be checked for proper oil return to the compressor, if not adequate do that before proceeding.

The Triple Evacuation Method is normally done on low-temp refrigeration systems, R-410a systems may require it on central air conditioning systems.

Pulling a system down to 50 microns will degas particles from the compressor oil; doing this will change the makeupand it will no longer be a good lubricating oil.

If you pull a 50-micron vacuum on the piping or another component other than the compressor with oil in it, the amount of extra time it takes to go from 500 microns to 50 microns may give you a warm and fuzzy feeling but the end result will probably be thesame as 500 microns held for 24 hours.

Another Viewpoint pdf: Triple Evacuation Method
First, remove any valve cores with a special  valve core remover this will speed up the evacuation time. Read & follow pdf procedures above.

1) Re-claim unit charge (Recover all the refrigerant)

2) Charge system to 150 PSIG with dry nitrogen and leak test

3) On contaminated systems replace the filter dryers. Then Repair all leak(s)

4) Evacuate system to 500 microns valve off & see if it holds 500 microns for 15 minutes, if it holds, break the vacuum with dry nitrogen

5) Evacuate system to a deeper 400 microns, valve off vac pump, & again break the vacuum with dry nitrogen

6) Evacuate system to 400 microns and & then Check to see if it holds. (Recharge with fresh clean refrigerant)

7) Check to see if the Supply and Return air ducts were correctly sized & sealed by the original installer.

If a vacuum pump will not evacuate a system below 1500 microns there is a problem with the pump itself, a leak in the system, or moisture in the system. Moisture is most likely because water vaporizes at 1500 microns.


Many HVAC contractors will consider this excessive time & effort for contaminated residential air conditioning systems, however it is a must for low temp applications.

The “micron” is a metric unit of measure for distance. The micron is a unit of linear measure; one micron equals 1/25,400ths of an inch. Modern high capacity vacuum pumps help speed up the evacuation process.
When a system has been evacuated below 500 microns, the pump is valved-off with the micron gauge connected, if the vacuum rises to 1500 microns and stops, there is moisture remaining in the system. If it rises above 1500 microns & continues to rise there is a leak. You should allow at least 15 minutes after the pump has been shut off an accurate micron gauge reading. When a system will not evacuate below 1500 microns there is either a lot of moisture in the system or there is a refrigerant system leak.
 
Sealing Sealing & Insulating the basement rim joists  - Excellent DIY Project - Make certain there is adequate combustion air for those type appliances!
Insulation & Weatherization Costs Forum
============================
HVAC Techs
This should be helpful.
CFM X change in enthalpy X 4.5, at 1000 feet above sea use *X 4.3 = BTUH (Ballpark) Operating Performance
"U Must Right Click Link & open in New Tab"

Wet Bulb Enthalpy Chart 
=================

DISCLAIMER:
I assume NO responsibility for the USE of any information I post on any of my Web pages,in E-Mails or News Groups.
All HVAC/R work should always be done by a licensed Contractor & properly licensed Techs! This information is only placed on these pages primarily for your understanding & communication with contractors & techs. This information is also for the edification of Contractors and Techs.
Never attempt anything that you are NOT competent to do in a SAFE manner! I am NOT liable for your screw-ups, you are liable for what you do! - Darrell Udelhoven

Cut Your Home Energy Use & Utility Bills in Half New

ACH - Air Changes per Hour - AVERAGING INFILTRATION RATES  - New

ENERGY WISE
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Excellent Illustrated Ways to Save Energy.pdf Save with/in Adobe Reader

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The Testo 416 Airflow Test Checking airflow - should always be performed before charging a system!
Description of 416 Testo Telescoping Vane Anemometer - A MUST
The Testo 416 Airflow Test Checking airflow

Air Flow CFM of a very large Supply Air Register using a Testo 410 Vane Anemometer  Basic...

Realtime HVAC A/C BTUH Performance Output (Part 1 of 2) YouTube Video

*Realtime HVAC A/C BTUH Performance Output (Part 2 of 2) YouTube Video

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HUNTING • SHOOTING • BALLISTICS TABLES • LEADING with RIFLES

Getting it right makes all the difference in the world.
This Energy Star ACCA pdf is interesting & confirms what many of us have been preaching, including educating the potential customers!

Scroll down to page 5 Market Conditions, & study to learn how we can all profit, customers included... 
http://www.energystar.gov/ia/home_im...ors/qispec.pdf

There are more ACCA links but this is a good starter document. 10/05/10

Residential Quality Installation Check List
 Use to pre-qualify Contractors

NATURAL GAS or PROPANE

  CFM = (Input BTU x thermal efficiency - Furnace OUTPUT) / (1.08 x temp-rise DT) or use 1.1

  Note: Combustion efficiency can be used in place of thermal efficiency.  

  DT is the temperature rise across the heat exchanger in degrees Fahrenheit 

  This will give you an approximate CFM; although it will be very close to the actual if the measurements are made accurately and the input of the appliance is correct 

  ELECTRIC HEAT

For an electric furnace the airflow measurement procedure is the same.  Allow the appliance to operate until the temperature rise stabilizes. Measure the temperature rise again out of the line of sight of the electric heater, along with the incoming volts and current draw in amps to the electric strip heaters.  Enter the information into the following formula 

  CFM = (Volts x Amps x 3.41) / (1.08 x temp-rise DT) 

  FUEL OIL
For fuel oil the procedure involves verifying the nozzle size and the correct fuel pressure.  After the Nozzle size in GPH (gallons-per-hour) is known and fuel pressure set to the listed data, the combustion efficiency must be measured with a stable stack temperature, and the temperature rise across the heat exchanger recorded

CFM = (Input BTU x thermal efficiency - Furnace OUTPUT) / (1.08 x temp-rise DT) or use 1.1



Darrell Udelhoven - HVAC RETIRED - udarrell

How we can reboot the private Sector Economy & HVAC work
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Darrell Udelhoven - (U-dl-hoven)
udarrell
Edited: 04/17/2014

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Darrell Udelhoven - Darrell Bloomington - Bloomington - Lancaster - Grant County - Wisconsin