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  1. #1
    Join Date
    Nov 2007
    Posts
    5

    Two cracked heat exchangers

    Hello
    I have the following situation:

    Summary:
    1. 3 level split house 1800 sq feet in the Seattle area
    2. In the last 8 two heat exchanger developed cracks .
    3. 8 years ago I have hired a local heating contractor to install a new gas furnace and got Carrier install. I don’t believe that salesperson did proper Manual-J sizing, but merely eye-balled the house, windows, etc to recommended proper sizing.

    The installed furnace is:
    Carrier 58RAV095, Input BTU 92000, 80% efficiency, therefore output BTU 74000.
    It may worth mentioning that during its 8 years inducer motor was replaced 3 times (two while previous inducer motor was on its own warranty)
    This is a second furnace with the crack, albeit a hairline crack.

    According to the rough estimate http://www.hvacopcost.com/equipsize.html the correct BTU for my house would be 79000. So the my furnace seems to be within the range.


    With all these said:
    1. Would what would cause 2 cracked heat exchangers in the course of 8 years? According to above reference furnace does not seem to be oversized
    2. Is there inherit problem with the Carrier 58RAV (keeping in mind 3 inducer motors which gone wrong)?

    The house is build in 1969, where there is no obstructions in the ducts, some rooms on the 3rd level have pretty poor airflow. I would attribute this to lack of proper design (too many 90 degree bends).




    Thanks,

  2. #2
    Join Date
    Apr 2004
    Posts
    7,680
    poor airflow, not changing filters, closed registers.... In otherwords, not getting the heat out of the HX.

  3. #3
    Join Date
    Nov 2007
    Posts
    5
    Hi

    I have electrastatic filters which are changed regulary. There are no closed registers.

    Is it possible to determine if airflow is bad or good? Can such determination be made by a heating company?

    First thing comes in mind is a measuring airflow speed in the plenum and comparing it with the furnace's recommended/nominal speed?

    Thank

  4. #4
    Join Date
    May 2005
    Location
    Western Kansas
    Posts
    267
    someone that knows anything about the trade should be able to take temperature and static pressure measurements and find the problem rather quickly. If you feel you aren't getting answers from this company, consider another after talking to friends and neighbors.

  5. #5
    Join Date
    Mar 2004
    Location
    SE Michigan
    Posts
    17,911
    Definatly an air flow issue either on return or supply or even both. Static pressure readings should be taken to find the problem. May be a venting issue as well.

    Can you post some photos?
    " Kill a Commie for Mommy! "

    - Colonel David Hackworth (1930-2005), Korean War Vet

  6. #6
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,181
    Quote Originally Posted by LeonBrag View Post
    I have electrastatic filters which are changed regulary.
    Do you really have an electrostatic filter, or do you have an electronic air cleaner?
    Perhaps you should have read the instructions before calling.

  7. #7
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    lack of combustion air can also be a factor with a cracked hx
    flame impingment from dust build up because of no servicing or not enough

    over fired because gas pressure wasnt checked

    air flo is a biggy

    there are many factors for a cracked hx that isnt near its life span
    a tech should be able to find the reason and retify it when the new furnace or hx is put back into service

    it is to late for the cracked one but not for the new one

    time to find the reason

  8. #8
    Join Date
    Nov 2007
    Posts
    5
    Sorry for the confusion, it's Electronic Air Cleaner 16x25. I had numerous techs from more then one company. None of them are interested in any real troubleshooting. They all propose:

    1. Change the furnace
    2. Change HX

    Is there a list I can give to the tech (or call heating contractors to perform checks), for example:

    1. Check static preasure
    2. Check termprature
    3. check if there is enough combasible air. Furnace is in the large crawlspace (tall enough to walk in), with only two crawlspace vents.

    Thanks

  9. #9
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    For a problem like this, I'd do a telephone search and find a company that can and will do a professional Manual 'J' calculation. You'll have to pay for it but it's money well spent. Now that you've found the company that does it correctly, you can reasonably assume they'll work with you got try and resolve your problems. They should have the checklist but you've summarized it pretty well to start with.

    1. Temperature rise
    2. Total static pressure
    3. Gas pressure at the manifold with all gas appliances in operation

    It's most likely that with just these readings, a good tech can pin down the problem. I've seen recuperative coils plugged so badly that very little air can get past them. That will show up as a high temperature rise. So just find the right company I think your problems will be short lived.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

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