Cracked Heat Exchange

Originally Posted By: phughes
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What is the best way to determine if the heat exchange in a gas furnace is cracked?

If your using a carbon monoxide checker, which brand and model do you recommend?

Originally Posted By: dbush
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The best way is to have an HVAC guy come in and take it apart.

Short of that, look for rust settling in the heat tubes, use a mirror to look at the bottom of the heat exchanger through the tubes, and watch for a "jumping" of the flames.

I use the Bacharach Monoxer II. I like it and everyone I have talked with prefers it over others.


Dave Bush
MAB Member


Originally Posted By: lwilliams
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What about checking all registers for soot residue? Not conclusive but usually an indication.

Originally Posted By: Blaine Wiley
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Look for flame roll when the blower motor starts.

Originally Posted By: rsummers
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Dave I think you are right the best way is to call the HVAC contractor out. I also use a Bacharach Monoxer II and think its the best. Some times its impossible to see a crack with out removing the Burners and that’s out of the scope of an inspection. Blaine is also correct with the distortion of the flame when the blower comes on. Unless you have the blower door off in a small closet the fan shouldn’t distort the flame. Its not an easy task some times locating a cracked Heat Exchanger and we all should probably state in our reports that we could not view the entire Heat Exchanger due to the fact that they are out of view with-out taking apart the furnace.

Originally Posted By: mmahurin
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I have just joined Nachi, and have been doing inspections for about a year. In reguards to Heat exchangers, our local news in Detroit has done an expose on “shady” Home inspectors. The thing that was most disturbing is related to the inspection of the Furnance area. They brought in some guy from a technical school and he did a pre-inspection on the home to see how the other 8 inspectors who where called in seperately not knowing they where being watched by a hidden camera by the reporting who was disguised as a home buyer. Long story Short, The instructor stated there was a crack in the heat exchanger which all the inspectors missed. However, the instructor removed or dissasembled a front heat echanger cover panel to expose the whole front of the heat exchanger to find this crack. Therfore, the other inspectors where not able to see it. My question is your not always going to be able to tell from a C02 test level of say less than 5 ppm if there is a crack? And would large amounts of soot build-up in the burner area also mean or assume you have a cracked heat exchanger? The reporter went on to say to a viewing audience of 2-million plus that a Home inspector should always visual check the heat exchanger, which was just wrong. So now I have customers who expect that, when I tell them it is not part of the required practices of ASHI, NAHI NACHI certified inspectors they question as to why. I also tell them you can’t believe everthing you hear on news storys’s because they are trying to create a story or sensationalize it. Plus we are not licensed experts for Heating and cooling and cannot legally dissasemble furnaces to view the heat exchanger completely. Any thoughts? Thanks Mike P.S. If any of you have a tried and proven check list or steps you use to inspect Forced air gas furnaces please let me know.

Originally Posted By: Greg Owens
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the way I understand it is you must have a heating and air license or work under someone who does in order to disassemble any part of a furnace. you should not claim there is a crack if you can not see it. how much rust would be excessive in a heat exchanger I have seen a furnace that had rust deposits covering most of the burners and having the service guy (who would get a commission if he could sell a new furnace) find the heat exchanger to be solid. soot around the grills? could have been a furnace that was already replaced, bad filter maintenance causing dust to hit the heat exchanger and burn, a dirty or worn out electronic filter. flames jumping are a sign but they also could be from inadequate combustion air supply, or leaky duct work.

The inspector is not required to Inspect or evaluate interiors of flues or chimneys, fire chambers, the heat exchanger, the humidifier or dehumidifier, the electronic air filter, solar heating systems or fuel tanks

if it is older or looks neglected recommend they have it checked by a HVAC company.

Originally Posted By: rsmith5
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I agree Greg, a freind of mine is a HVAC specialist and says the only way to tell for sure is to dismantle the sheetmetal to look at the heat exchanger. Anything less would be fool hardy. He mentioned the same explanations for the clues[soot at registers, jumpy flame and rust] that were sugested in the earlier posts. He also added that if the unit was over 5yrs, dirty, rusted, or if you have any suspicions to have it checked by a pro. Imagine the bad rep from stating that the exchanger was cracked or good and having a pro prove you wrong! Like everything else in our profession, you have to be sure or refer to a pro.


Originally Posted By: cbottger
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I too am new to NACHI but not to the HVAC and Heating business recently retired after forty years in the business.

And as an Hi for the last 7 years I do not disassemble furnaces to inspect heat exchangers I follow the standards of practice for Hi’s.

I would agree with most of the above posts as to detecting faulty exchangers. There is no way with out dissembling to be perfectly sure.

I use a CO detector that Measures .001PPM and I am of the opinion that all HI’s are doing a disservice to their clients if a CO test is not performed

on Fossil fuel furnaces even if it is not required by the Standards of prac tice. The standards do not state that HI’s can not go above and beyond what is required. CO Meters should be in all HI’s tool kit as it is a much better device than what was used when I was a pup. Can remember using 2 tablespoons of salt in your hand thrown into the blower wheel of of the furnace and watch the flames go crazy on the burners with a cracked heat exchanger. I don’t recommend this as salt and metal don’t get along to well.