Heat Exchange

I just read the "How are you inspecting HVAC units and found some of the answers very interesting to say the least. Almost afraid to post this question but thought I would really like to hear from sincere inspectors. How do you inspect the heat exchange on a furnace? Seams many of you are not but this is the most asked about part of a furnace operation from my customers and seams to be very important as to its proper functioning. Those of you who do a thorough inspection of the HVAC, please respond. Thank you in advance.:roll:

Well one thing about this BB is you will never get a answer to any question if you don’t post.
There is very little one can see doing a visual inspection of a heat exchanger. Bora scopes and or carbon monoxide detectors are the basic tools but they are not 100% by any means. I have found many cracked exchangers with the carbon monoxide detector but no telling how many I have missed with just small cracks that did not show up the day of inspection. Disclaim unless you are qualified and licensed to remove the exchanger cover.

Furnaces last forever here, AC is what breaks.

If a crack in a heat exchanger is really bad, when the blower kicks on it will try to blow out the flame on an older furnace. Also the newer furnaces are suppose to shut themselves off if the heat exchanger cracks by use of pressure switches when the crack is heated and opens up. Now the Lennox Pulse furnaces sometimes did not shut themselves off when the heat exchanger cracked, thus they are no longer in production.

Do you have a link or other info on these safety devices?

Thanks Charley,

When you do a basic home inspection, what exactly do you inspect as far as the furnace goes? The carbon monoxide test you were refering to in yor answer, what kind of detector were you using? And finally, do you have a copy of the disclaimer you use?

What and How I inspect basically depends on the type of furnace pertaining to gas fired most common in this area. I pull the front cover and watch the flame pattern like to see a nice blue flame. On the older type open burners I look for evidence of flame roll out any burnt or scorched metal and or wiring exterior to the burner chambers. The amount of rust build up in the bottom of the burner chambers some times I see the burners partially covered with scaling rust that has dropped down from higher areas of the exchanger blocking the gas distribution of the burners.

If the furnace is really old I have in the past pulled one of the low voltage wire spades and re-connect from the top of the gas valve so that I can actually observe the flame during the ignition to see the amount of roll out.

A biggie for me is I stay with the furnace after I have turned the stat out of the heat mode and determine that the blower does indeed cycle off after the burner shuts down. Another biggie for me is I ensure the burner is not cycling on and off on a safety or limit switch before it reaches the set point of the stat I see this on a frequent basis and the home owner is not even aware of it.

I use a Fluke CO meter

I myself do not use a standard disclamer I use a simple statement Like (The furnace was operated at the time of inspection through a normal cycle and was performing as intended but should be considered as having exceeded an average life expectancy for this type of equipment and recommend you budget for its replacement)

Rip open a dozen heat exchangers without using a screwdriver.

How? Check this out!

Coming soon…

I look forward to going through the coarse online, when available.


I question the idea of providing such an invasive inspection of a typical HVAC system, as part of a standard H/I, under the SOP as existing, and as I understand it. This additional amount of technical education and/or service provided to the customer by you/us may/could be a “pandora’s box” if the H/I goes bad, and you end up in court.
I visually inspect the exterior/interior of the Furnace/AHU, typically noting the Mod.& Ser.#'s, and commenting on the basic physical conditions, and on the basic system cycle. I interpret my findings, limited as they may be, and I usually recommend that the unit/system be further inspected by a Prof. HVAC Contr. IMO

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