Oil Furnace Heat Exchanger Soot Cleanout

    - with Darrell Udelhoven Darrell Udelhoven

  Important Critically Necessary Human Health & Safety Servicing Procedures

HVAC Contractors, you had better learn to do these important service procedures in the proper way...
Micro energy economics

Please Respond on my Blog; let me know if you can't post: Oil Furnace Conundrums - Blog

Oil furnace pump filter/screen servicing video: https://www.youtube.com/watch?v=G_78-rh2He4

Oil pump pressure should be checked every year, especially if Btuh Output appears to be low - Video: https://www.youtube.com/watch?v=vPWXDtAmjyU&src_vid=G_78-rh2He4&feature=iv&annotation_id=annotation_723453

Oil furnace delayed ignition Video: https://www.youtube.com/watch?v=J__bOVzn8Ig

Very Good Video of thorough Oil Furnace Servicing: I book marked it but could never find the video again; no trace!

Wrong Video: http://yhoo.it/1tIsY9M 

A badly sooted interior of an oil furnace heat exchanger can be very costly & even deadly.
How many contractors that you know, are doing this procedure right, or that have the proper cleanout tools?

  • Clean the furnace flue pipe, barometric damper and chimney base.

  • Barometric dampers are shipped with the weights on the right side for vertical flue pipes; for horizontal flue pipes the adjustable weights must be switched to the left side; rough weight adjustment is usually for -0.04 to -0.06" draft. Never seen one switched!
  • Check the condition of the furnace heat exchanger.

  • Removing soot buildup from the heat exchanger interior cavities. Use extra long heat exchanger brushes of the correct diameter and a shop-vac with a ten foot long & one inch diameter hose, to remove soot buildup from Thermo Pride OL11 heat exchanger cavities. Brother's went 31 years & HT-EX never cleaned or fuel pump strainer never cleaned or replaced!

  •  These are difficult to reach in many oil furnaces, and it takes patience and perseverance to do a good job on a HX. (Extremely Important for safe performance and efficiency; & to avoid CO poisoning, etc.

  • The PRO Technician needs good instruments to test the various draft aspects of an Oil furnace; after it has been operating for around 10 minutes to sufficiently get the walls of the combustion chamber white hot.

     If any of the three fuel oil filters leading including the one at entry to nozzle are plugged to much the furnace may NOT produce the required combustion heat to operate within the equipments' human safety requirements...

    All these tests call for a well qualified Oil furnace PRO TECH knowledgeable Specialist.

     The overfire test is performed first by locating the over draft access port; if none; by drilling a 1/4 inch hole in the pressure relief door over the burner; often called the observation door.

    Start with a barometric breech flue pipe damper draft control setting of -0.04" may need to use -0.06" of W.C. to get required over-fire draft.

     The flow rate of the heat exchanger must be taken into account for proper burner operation. By measuring both the overfire draft & flue pipe stack draft resistance on a new oil furnace, the design draft resistance can be determined.

     The difference between the overfire draft & flue pipe stack draft will be the heat exchanger (HX) draft flow resistance.

     When checking the units performance if after a period of years of opertation, if the heat exchanger flow resistance has nearly doubled, it is necessary to mechanically clean the heat exchanger flue passages.
     HX resistance is the difference in draft from the outlet of the furnace to the overfire draft.

     Example, you install a new furnace and measure a flue stack draft of -.05” and an overfire draft of -.02“. This means the pressure drop across the HX is -.03“, so you notate that on the ticket. You go back 2 years later and the now you have a stack draft of -.05“, however, the overfire draft is now -.00“. This means the pressure drop increased to -.05” vs., the -.03”, (or increased .02” WC) from when new, telling you there is added restriction (usually soot).

     Another way to tell is to notate the stack temp when tuning a furnace. If you have 500 with a clean HX and a year later you have 700 at the same firing rate and air adjustment, you know there is a layer of soot insulating the walls of the HX.
    - chuckcrj - on HVAC-Talk.com 01/19/13
    A negative pressure must be maintained on the heat exchanger to prevent the products of combustion from being forced into the occupied area.

    Those fumes carry soot & CO carbon monoxide; a dangerous situation!

    You need the help of a real Oil Furnace PRO...
Check the chimney setup: A chimney must have good air circulation at its opening to function properly. Some backdrafts result from external obstructions blocking or interfering with air movement around the chimney. A large tree within 30 feet of the chimney, for example, might result in poor air circulation and a resulting back-draft. Also, nearby buildings might interfere with air flow in the chimney's vicinity. Extending the height of the chimney top can often solve the problem, as taller chimneys draft more efficiently than shorter ones.

A strong wind may interfere with the chimney's ability to retain an effective updraft. The design of the chimney cap may also cause drafting problems. Special types of chimney caps, however, can take advantage of the wind to eliminate back-draft. These caps consist of two hoods positioned to guide the wind around the unit. As the wind goes around the cap, it creates an updraft, drawing smoke and gases from the chimney.

"Getting it RIGHT, - makes all the difference in the world."

All installations and services must be performed by qualified service personnel.
4. With access to the inside of the heat exchanger through the burner cleanout openings and the vent pipe connection, it is now possible to use a long, flexible wire brush and an industrial-type vacuum cleaner to remove any soot build-up.
NOTE: A one inch (outside diameter) vacuum cleaner hose will fit into the radiator.
To vacuum and brush the outer radiator of the heat exchanger, go through the cleanout openings in both directions, as shown in pdf.
This is the best Thermo Pride instructions for cleaning soot from the oil heat-exchanger Go to Page 10 on the linked pdf
Here it is, the graphics for cleaning Thermo Pride heat-exchangers  tools required  scroll down to, or type in 16 & hit enter.
Oil Furnace Heat Exchanger Cleanout Procedures- Service Techs
View the graphic on the pdf where you can read it.


For a number of reasons oversizing an oil furnace is worse than oversizing a gas furnace. An oil heater needs longer runtime cycles to reach a high enough operating temperature to effectively burn the carbon molecules. In addition, the nozzle needs to be sized within 10% of the rated capacity requirements of the refractory so its white-hot surface can reflect the right amount of heat to effect the burning of carbon.

At an oil burner startup, the combustion process is poor & unburned carbon flows through the heat exchanger. For the first 90 seconds until the refractory (combustion chamber) comes up to temperature soot is deposited everywhere.

This is another reason why you need to keep all the filters & screen/strainers, especially the one inside the pump’s housing, changed out & kept clean for an optimal adequately hot efficient refractory fire.

The above is also, why I like the Temperature SWING Settings of some programmable room thermostats so you can increase the cycle runtime lengths for better efficiency & longer higher performance of oil heating equipment


Contractors, here is one place to get the pump inlet fuel/oil strainer/screens with gaskets

Suntec A series strainer and gasket -
This screen should work in Suntec A2VA -7116 & other Suntec oil-fuel pump inlets

YouTube Video on changing out the pump strainer screens  PROs Only - Other videos on Oil burner servicing
Suntec A series strainer and gasket    Goto website to buy 66-340
photo of item KSS#66-340

This `Suntec A series strainer and gasket` can be substituted for some Suntec OEM part numbers:

Don't have printed catalog, just the website.

I have to lay the major responsibility on the oil furnace mfg'ers for the oversight of the field Techs.

Mfg'ers do not provide the blower graph or list the pump inlet strainer/screen or a part#, they never explain that the belt-drive quarter HP blower motor is nowhere near up to providing enough airflow for an A/C installation & that a direct-drive multi-speed higher HP motor is mandatory for both heating & cooling modes.

Also, they don't state that the A/C evaporator coil needs to be installed at least 6 inches above the Oil furnace; as other mfg'ers do state.

 These are mandatory instructions & information that ought to always come with the Oil furnace.


The Performance Data on Carol’s Oil Furnace Situation - 12/08/12

The initial acute problem is extremely low blower airflow across the heat exchanger &, also through the evaporator coil during the summer cooling mode.

Then we have combustion air that was set excessively high causing lowered heat output. Add to that the partial plugging of the oil line filter screens & that is another drop, which will be shown in my testing data below.

When it was new, or after the first service, an .85 GPH (Gallons Per Hour) nozzle was installed; #2 diesel fuel produces 140,000-Btu per gallon.

140,000-Btu * .85% is 119,000-Btuh Input; the furnace only gets around .75% or less efficient Output now, compared to 80% when first installed.

119,000 * .75 is 89,250-Btuh Output now, or less, if delivering its full 100-psi fuel to the burner, which my airflow test indicates its not doing, probably due to the little known & attended to inlet screen/strainer to the fuel pump.

The blower airflow test meter indicated around only 500-CFM of airflow when 900-CFM (the 2-Ton evaporator coil’s top CFM) will not keep temperatures within reasonable parameters. 89,250-Btuh Output / 900 is 99-F temp-rise over 70-room-temp is 169-F at closest supply air register, even at 900-CFM that is yet too high/hot.

*OK with a new 95% 57,500-Btuh Output Propane furnace; 57,500 / 900-CFM is 64-F; only 4-F over recommended temperature-rise; with 3-Ton blower; not a problem as we can go some above 900-CFM evaporator limit for cooling mode, when in the heating mode.

At the projcted 450-CFM; & that fuel oil pump strainer/filter screen replaced; = 89,250-Btuh Output / 450-CFM is 198-F; that high a temperature is unallowable; limit is set at 200-F.

After adjusting air to the burner, Btu output increased a lot; here are those increased temperature figures using a digital thermometer. Maximum temperature at that best airflow kitchen register on Monday 01/14/13 was 157-F; room temperature was 60-F temperature rise was 106-F which is way too high due to low airflow. also, the airlow CFM is only around 450-CFM * 106 is 47,700-Btuh

The formula: 97-F * 1.1 is 106.7 * 450-CFM is 48,015-Btuh; evidently due to that undetected fuel pump filter screen restriction. Therefore, 89,250 - 48,015 is a loss of 41,235-Btuh due to that filter/screen restricted fuel line flow to the burner. 


Well, the last test output capacity was 43,280-Btuh; should be 89,250-Btuh.

The very low blower airflow will NOT allow me to get this oil furnace setup to work properly no matter what else I do to get optimal performance from the oil burner!

Most new lower output oil furnaces are lower in height therefore a transition would put the coil well above the oil heat exchanger for much better airflow at a lower static pressure.

When I closed the secondary combustion air setting, the fire got a lot hotter & the furnace has not gone off on the safety manual reset since then.

 However, I don't trust it to keep running as it seems to take way to long for the oil pressure pump to get it above 80 psi so the burner will fire in time to prevent the safety cut-off. Seems it should only be a few seconds...probably partially plugged pump inlet strainer...that strainer has never been serviced in 31 seasons, only the tank filter & that not nearly as often as it should have been.
I have to lay the major responsibility on the oil furnace mfg'ers for the oversight of the field Techs.

Mfg'ers do not provide the blower graph or list the pump inlet strainer/screen as its part#, they never explain that the belt-drive quarter HP blower motor is nowhere near up to providing enough airflow for heating when there is an A/C installation & that a direct-drive multi-speed higher HP motor is mandatory.

Also, they don't state that the A/C evaporator coil needs to be installed at least 6 inches above the Oil furnace; as other mfg'ers do state.

 These are mandatory instructions & information that ought to always come with the Oil furnace.

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!

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

Also, at 700-rpm & only .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!


Any of the HVAC companies I list on any of my web pages have nothing to do with the information I post on any of my Web pages nor do I assume any responsibility for how anyone uses that information.
All HVAC/R work should always be done by a licensed Contractor! This information is only placed on these pages for your understanding & communication with contractors & techs.

This information is for the edification of contractors and techs. I am NOT liable for your screw-ups, you are liable for what you do! - Darrell Udelhoven

Darrell's Refrigeration Heating and Air Conditioning - Federal Refrigerant Licensed - Retired Licensed Contractor

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Darrell Udelhoven
Posted: 08/06 | Revised 09/27/13