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  1. #1

    Question Cracked Heat Exchanger

    I just had my fall furnace check by my HVAC contractor. The tech told me he had to red tag our furnace because we had a cracked heat exchanger. He showed me how he put a little bit of puffed smoke into the heat exchanger and it swirled around and some came out. He said air backflow means the heat exchanger is cracked. From then it was high pressure sales to replace the furnace and, by the way, while we're at it, why don't we replace your ac as well?

    Being a conservative homeowner, I got a second opinion. This contractor laughed at the idea of a smoke test. He used a CO detector and registered no CO, so he said our furnace was fine.

    Being curious, I've started doing some reading and I'm finding conflicting ideas on how one should check for a cracked heat exchanger. Would anyone care to elaborate on what sort of tests or checks should be done for a cracked heat exchanger?

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,742
    Visually check if accessible or with a snake camera, and a combustion analysis with a high tech tool. I'm not sure what the smoke test was but most furnaces now have a fan induced draft so if you put smoke to it it would pull it up the vent. Sounds like the guy was trying to make some commission to me but CO is nothing to mess with so I would invest in a couple of these its cheap life insurance http://www.nationalcomfortinstitute....mer%20Products the ones sold in home improvement stores are not sensitive enough to protect your family.

  3. #3
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    On the pro side a one of our members found a guy dead next to his boiler last week. Definitely spend some money on CO detectors.

    How old is the furnace?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  4. #4
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    producing no CO does not mean the heat exchanger is not cracked...... not sure what the smoke test was all about.....
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  5. #5
    JTrammell - Neither tech used a camera. What type of equipment would be used for a "combustion analysis with a high tech tool?" I've been checking into CO detectors. I'll look at your links.

    TedKidd - the home is a spec - the furnace was installed 8/02. We purchased the home 4/03. It is a York Diamond 90 upflow.

    By chance the 2nd techs company distributes York. (BTW - selected this tech based upon informal survey of friends via FB - they were very highly recommended). First thing they did was check the warranty and told me upfront the heat exchanger had a lifetime warranty.

    When the 1st tech was questioned about this, he wouldn't give a straight answer. Also found out 2 neighbors were waiting for parts for their heat exchangers (American Standard) with the same first company. One had been red-tagged for 7 weeks! Didn't do much for my confidence in that company.

    Bottom line for me is my family's safety. If neither test is a good one, what should the tech be doing?

    Thoughts on calling the gas company for a 3rd check?

    PS - here is what the first contractor had to say via email about the smoke test:
    I do feel it necessary to talk about our smoke test versus the carbon monoxide test. Detecting carbon monoxide in your ductwork after it comes out of your furnace is certainly a great indicator that there is a crack in your heat exchanger. However failure to find carbon monoxide in your ductwork is NOT proof that you heat exchanger is in good working order. Your 90% gas furnace has a powered vent which draws combustion gases, containing carbon monoxide, through the furnace and expels them out the flue. A heat exchanger would have to have a dramatic fault in it for the carbon monoxide to escape into your supply air. We prefer to find these leaks BEFORE they become a health hazard, with a smoke test, not just any smoke test and I will tell you most of the smoke test equipment on the market is laughable. We have found a rather expensive smoke test device that preforms very well. We follow this smoke test up with another device called a magnehelic, this device measures pressure or air current within the heat exchanger. I‘ll stop the complicated explanation of how this procedure is preformed and simply say it is one that has been approved.
    Any comments? What is a magnehelic? The tech didn't do any other tests.

  6. #6
    Join Date
    Jan 2010
    Location
    Toronto,Ontario Canada
    Posts
    355
    Life time warrenty isnt our life time warrenty. Dont get that confused. life time warrenty for a furnace is 20 yrs. A furnace should be updated every 15-18 yrs to keep it efficient. But i have seen furnaces in the late 30's that dont have any problem with them but they are extemely old and not effient at all.

    Some times you just have to believe your local gas company for their findings and i do admit, i have had times where i wasnt sure so i called in for a second opinion. Good companies do that without any questions. If your furnace is in its late teens its probably time for a change. One thing that helps a furnace last longer without any break downs most of the times are 2 simple things

    -changing filters often 4-6 times a year
    -get it checked out every year or so.

    Good luck and have a warm winter
    Last edited by akelesis; 10-31-2012 at 11:18 AM.
    Get er Done!

    Do what has to be done
    when it has to be done
    as well as it has to be done
    And doing it all the time.

  7. #7
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    Quote Originally Posted by akelesis View Post

    -changing filters often 4-6 times a year
    -get it checked out every year or so.
    -properly size equipment.


    Equipment is often rated in cycles. So "undersized" equipment tends to last A LOT longer because they have fewer cycles per season AND run cooler. Oversized equipment will often bump "high limit". This overheating significantly increases stress on metal parts (causes cracked heat exchangers).

    Oversized equipment is further stressed by often being attached to ductwork that may be sufficient for properly sized equipment but severely chokes oversized equipment.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  8. #8
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,186
    Quote Originally Posted by tedkidd View Post
    -properly size equipment.


    Equipment is often rated in cycles. So "undersized" equipment tends to last A LOT longer because they have fewer cycles per season AND run cooler. Oversized equipment will often bump "high limit". This overheating significantly increases stress on metal parts (causes cracked heat exchangers).

    Oversized equipment is further stressed by often being attached to ductwork that may be sufficient for properly sized equipment but severely chokes oversized equipment.
    +1. Furnaces are perhaps the worst about being oversized. Contractors are scared of changing the way of thinking thats been around since the 60s. The minimal wholesale price differnce between a 50k and 100k furnace doesnt help either. Some funaces got oversized to get larger blowers to accomidate oversized ac units.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,879
    Many cracked HEs dont put CO into the air stream. Further investigation is needed on your furnace.

  10. #10
    Join Date
    Jun 2009
    Location
    Upstate SC
    Posts
    1,439
    The email he sent you is a legitimate check. He is correct for the most part. You can detect a cracked heat exchanger several ways. A crack in the exchanger will cause several issues. It will allow the indoor blower to leak air into the heat exchanger and have a negative effect on combustion. It will eventually cause the furnace to stop working because of safeguards that are in place. A cracked heat exchanger should be replaced. PERIOD.

    Some furnaces are designed in that a crack in the exchanger will allow CO to be pulled into the living space, not saying yours is though.

    Just because you can't detect the CO doesn't mean the heat exchanger has not failed.

    Sent from my ERIS using Tapatalk 2

  11. #11
    Join Date
    Aug 2012
    Location
    North Dakota
    Posts
    518
    theres an old school test called a lithium-bromide test (a liquid is spraied into the flame and an instrament in the airflow will detect it) ask for this over the phone then should it fail a visual inspection will be warranted

  12. #12
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,317
    Wouldn't a combustion analyzer pick up a cracked heat exchanger; say when the blower starts up the numbers change notably?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  13. #13
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,057
    Seems to me a 10 year old 90% furnace unless there's special circumstances, is a good candidate for replacing the heat exchanger under warranty. It surely should have been presented as an option. Of course the salestech who also thinks you should change a perfectly good A/C won't make his quota coming up with a HX swap. Nor will he likely make as much money doing the swap as selling an expensive system.

    With a strong draft inducer, a crack is very unlikely to let flue gases into the air stream unless the crack/hole is huge. Most new furnaces burn with 10-15 PPM in the flue gases so in order to have enough CO in the airstream to be detectible among the huge volume of air passing by, you'd really have to gave a problem.

    Last winter in training, we drilled holes in a heat exchanger. A combustion analyzer didn't notice any change.

    Those HX are tubular, shouldn't be that hard to find a crack visually. Maybe time for a camera.

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