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  1. #1

    Furnace burning smell

    Hi, I hope someone will be able to help.

    A couple nights ago, our furnace stopped working in the middle of the night on a very cold night. I checked out the fusebox and noticed that I needed to reset the breaker for the furnace.

    The house was at 58 degrees F at this point.

    I reset the breaker, replaced the filter, turned everything back on and went to bed.

    Around 3 hours later, after the heat had reached 70 degrees again, we noticed a smell like burning plastic.

    We called someone to check it out. He saw that there was condensation (forget where) and he had to replace a gasket in the furnace.

    He said the fuse problem was likely a short due to the condensation and that the burning smell was likely burning dust.

    But it's now 24 hours later, after the new gasket, and we still have the burning smell. Also, it seems like the furnace is starting up and stopping more frequently than normal (though we are still maintaining the temperature we set)

    Is it feasible that it's really just burning dust? If so, how long will it take for the smell to go away? The smell gets stronger at the end of the cycle.

    Any other possibilities for the smell?
    Thanks,
    Andy

  2. #2
    Join Date
    Sep 2006
    Location
    Montana
    Posts
    983
    Quote Originally Posted by Kwak View Post
    Hi, I hope someone will be able to help.

    A couple nights ago, our furnace stopped working in the middle of the night on a very cold night. I checked out the fusebox and noticed that I needed to reset the breaker for the furnace.

    The house was at 58 degrees F at this point.

    I reset the breaker, replaced the filter, turned everything back on and went to bed.

    Around 3 hours later, after the heat had reached 70 degrees again, we noticed a smell like burning plastic.

    We called someone to check it out. He saw that there was condensation (forget where) and he had to replace a gasket in the furnace.

    He said the fuse problem was likely a short due to the condensation and that the burning smell was likely burning dust.

    But it's now 24 hours later, after the new gasket, and we still have the burning smell. Also, it seems like the furnace is starting up and stopping more frequently than normal (though we are still maintaining the temperature we set)

    Is it feasible that it's really just burning dust? If so, how long will it take for the smell to go away? The smell gets stronger at the end of the cycle.

    Any other possibilities for the smell?
    Thanks,
    Andy
    I doubt it is burning dust unless you haven't ran the furnace in 6 months. When the tech came out to replace the gasket, did he do anything else or just walk out the door? What was the gas manifold pressure? What was the temp. rise on the furnace? If he didn't check any of this stuff out, he needs to come bag on his dime and find your problem. You already paid him and he didn't fix it the first time.

  3. #3
    Join Date
    Jul 2010
    Location
    SE Texas
    Posts
    122
    Quote Originally Posted by big sky hvac View Post
    I doubt it is burning dust unless you haven't ran the furnace in 6 months. When the tech came out to replace the gasket, did he do anything else or just walk out the door? What was the gas manifold pressure? What was the temp. rise on the furnace? If he didn't check any of this stuff out, he needs to come bag on his dime and find your problem. You already paid him and he didn't fix it the first time.
    Ditto,

    The only time you will really smell burning dust is when you fire it up for the first time for heating season. Even so, the smell usually goes away in less than an hour. A "bad gasket" is kind of a reach IMO, sounds like he really didn't check anything else.

  4. #4
    Join Date
    Apr 2010
    Location
    southern california
    Posts
    535
    Dust no way, get your tech out there again before you need the fire dept. My guess is the blower motor, I would feel the motor after it has ran for a few minutes and see if case is too hot to touch. Obviously an infrared thermometer would work better than your hand. Unplug the furnace before reaching into blower section.

  5. #5
    Join Date
    Feb 2011
    Posts
    75
    Is this a Carrier furnace? Some models had secondary heat exchanger with a plastic coating that over time will begin to fail and melt, closing off heat exchanger cells. Blower moter does sound like it fits the bill, but I would assume that if you had a contractor out they would have checked this with an amp draw.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    A burning smell and a tripped breaker? Not good.

    If the tech does not KNOW why there was a burning odor, he hasn't found the problem. Apparently the gasket replacement did not solve the problem, as you still smell it.

    Nature of the burning odor...like something electrical burning? Wood smoke smell? Burning plastic? Rubber?

    I know it's cold out, but I would shut off the furnace and get this checked out ASAP. A cold house is better than a house that's nothing but a pile of ashes.
    • 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.

  7. #7
    Join Date
    Jan 2010
    Location
    Hunts. Al.
    Posts
    356
    I was thinking burning windings right off the bat. What gasket are we talking about?

  8. #8
    Join Date
    Feb 2011
    Posts
    75
    Start isolating systems to determine the location of the smell (not that any HO should ever have to do there own diagnosis). Run the fan only for a while and see if the smell is there or not, then run the furnace and smell what comes out of the exhaust pipe (you mentioned condensation so you should have an exhaust pipe out the side of your house somewhere) and try to determine if the smell is on the air distribution side or the combustion side.

    Seems most are in agreement that it sounds like a blower motor, but we would all have to think the first company checked that. If they replaced a gasket on the exhaust motor that was starting to melt it is due to too high of temperatures in the exhaust.

  9. #9
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,934
    Whoever you had come out to check things didn't do their job IMO. Found the first thing that was glaringly obvious, took your money and left. That is if you told them what you've said here.

    A circuit breaker tripping is a serious indication of something wrong. Smelling burning plastic is not dust....... that is unless your home for some reason is filled with plastic dust.

    If the person that came out is a technician from an established company, call the company and talk to the service manager or owner and explain what you have here to them. If they agree with what the technician said, I'd call someone else.

    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  10. #10
    Thank you for all your replies. We had a different technician from the same company come over. He changed three things, the gas valve, the motor and the battery like part that gives the fan a boost while starting (I forget the name). He said the fan wasn't coming on so the heat exchange was over heating.

    The good part for us was that the first guy gave a good sales pitch for the protection plan and we bought it so we got all today's repairs for free.

    The smell still lingers in the vents but doesn't seem to have new stink.

  11. #11
    Join Date
    Apr 2010
    Location
    southern california
    Posts
    535
    Quote Originally Posted by Kwak View Post
    Thank you for all your replies. We had a different technician from the same company come over. He changed three things, the gas valve, the motor and the battery like part that gives the fan a boost while starting (I forget the name). He said the fan wasn't coming on so the heat exchange was over heating.

    The good part for us was that the first guy gave a good sales pitch for the protection plan and we bought it so we got all today's repairs for free.

    The smell still lingers in the vents but doesn't seem to have new stink.
    Blower motor, run capacitor and gas valve, did he explain why he had to change gas valve. Only reason I am asking is it would be unusual to find those components failed at the same time. Refering to gas valve

  12. #12
    He said he changed the gas valve because it was letting in too much gas. On ignition it was more explosive than it should have been and the furnace shook.

    Also, he said that he was just changing the motor becuase if he didn't he figured someone would have to come back in the next month to do it.

    The furnace is 15 years old.

  13. #13
    Join Date
    Apr 2010
    Location
    southern california
    Posts
    535
    Ok , I think the previous tech played with the gas valve, or that was the original problem, the blower motor typically last about 10 years. I hope you have fixed your problems. A furnace changeout may have been in order do to the age and expense of failing parts down the road. The warranty you have purchased may be a good idea if it is not costing you more than a new piece of equipment. The life of a furnace is about 20 years.

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