Cracked heat X ????

[jjbergeron77]

If a newwer furnace has an issue with the heat exchanger it is definately a major problem. It does not take much for the furnace to start sooting up from an impropper air fuel mixture. A combustion analysis will tell you if there is an issue with the heat exchanger. Oxygen, carbon dioxide, carbon monoxide, excess air, and efficency readings should be within range. Any air being sucked in the crack instead of the primary inlet will cause issues.

[HuNGRYTeCH]

A combustion analyzer is a great tool but will not always tell you that there is a cracked hx. If the crack is large enough you definetly will have readings out of range but if it's just starting to crack, around an eyelet, out of your air stream, etc. You might not see it with a combustion analyzer. Learning how to do a proper visual inspection for different hx's is invaluable. All hx's have certain places they will fail first and is good to know.

[LibertyTree]

I look at the duct first, if the returns are piss poor and its an old Payne (the most common 80's furnace around here) I'm usually pretty certain there is a crack, or cracks. I keep nice looking 14X14 patches on the van so I can cut a hole in the plenum to visually inspect the HX if its an upflow, if its a downflow I will pull the blower and climb into that somb!tch. There are many times you wont see a crack with an inspection camera that you would see with your head directly above the HX

[crazyjohn]

what is the max recommended for co ppm?

[LibertyTree]

what is the max recommended for co ppm?

0.0

[chuckcrj]

what is the max recommended for co ppm?

99 and stable.

[red_oktober78765]

Just had one today. A Duomatic Olsen condensating nat gas furnace...Looked like a tech before me had cut the sheet tin on the furnace itself up near the plenum, looking for a bad hx, then plated it. the condensate pump was laying on the floor, with the top half seperated from the bottom half and the drain line off the furnace was in a bucket. The furnace had a spark-ignited pilot module and was tripping out and it looked like the A/c was added as an after thought by the wiring of a relay and other componenets inside the furnace...Hx had rust spots in it so I failed it on the basis that the H.O. would have been throwing good money to bad with me trying to get it going again then find out it had a bad hx anyways with flame roll out. Basically The time has come to start over with the heating unit. It wasn't designed to do what someone was making it do in the first place and now it needs a possible couple hundred dollar control module...Time to do things right.

[smoke]

Combustion analyzer, works sometimes.
Visual inspection, works better.

I have noticed that 18+ year old furnaces were built much better. I have come across 20+ year old Yorks that I tried to find a crack and couldn't. The heat exchangers were built better "back in the day".
I always find my cracked heat exchangers on the appliances that are 10-15 years old. Sometimes just due to age and sometimes due to an oversized furnace or incorrect A-Coil/plenum on top restricting air on the outer most cells of the exchanger.

Another trick that was told to me by a gentleman that has been in the business for quite some time is,
while the furnace is running and heating, use a spray bottle and mist a brine (salt water) solution into the intake of the fan. As you do this watch the flame structure. If there is a crack you will see the flames change.

The biggest cracked heat exchanger I've ever seen on a residential was a 15 year old natural gas. I pulled the blower assembly, laid on my back, wiggled inside and when I turned on my flashlight I didn't even need my mirror. It was 10 inches long, in plain sight and in the center it was about 1/4 inch of separation.

You can usually take the back panel off of oil furnaces to inspect. It's only like 20 screws...


~smoke~

[grasshopper]

Furnaces have all ways been in a negative pressure... It's not co spilling out of a crack that should worry you. It's flue gases backing up due to air being Pulled in brought the failure causing high levels of co or flame roll out. According to the AGA....ANY failure is well enough to red tag a furnace

Not true.... there are some furnaces that are positive pressure.

[cowboyfan628]

get the book from heat exchanger experts. better yet get your company to bring him in for training

[markvilleman]

If I got CO reading 10 ppm at supply air,I would red tap it. If the reading smaller than that, I would checked the condition of the furnace. I might use smoke candle to double check.

[Gross]

Not true.... there are some furnaces that are positive pressure.

which ones?

[cowboyfan628]

which ones?

only lennox pulse that I can think of