My furnace started to smell electrical fire once in awhile (not consistent). I guess it happens when we run the heat for a long time (many continuous days during cold weather). However, the furnace still works while smelling. I also notice sometime it has weird noise, like stalling "beeeeeee" noise. Here is the recording:


I am not sure if it's like that before or now I am starting to realized.

The filter was new and I installed it with exact airflow direction (left-to-right). When I smelled the first time and started to open the cover, the old filter popped out from the metal engage ring thing. It didn't fall off completely or touch any metal part to burn or anything (meaning the smell is not from the old filter).

Also while the burner is firing, I saw a metal stick at the direction of the fire and it's turning red. I am not sure what is the purpose of that stick (temperature sensor?).

I did some research from https://www.angieslist.com/articles/whats-funny-smell-when-heat-turns.htm and blog.snyderac.com/blog/be-cautious-of-these-3-furnace-smells so I came to some initial thoughts:

  1. My capacitor is probably bad and needs replace? Where do I find it?

  2. I might have install the filter in the wrong airflow direction?

  3. Some other electrical or crack inside that I don't see?

Before I call some contractor, I'd like to see if I can easily fix this. Please let me know your advise.

Top left

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Entire furnace open

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Red circle is the burner. Blue circle is the metal piece sticking out.

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Bottom part with new air filter (installed with arrow left to right)

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Just a view into the bottom (fan on right)

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Electrical switch

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The make and model of this furnace is Bryant Plus 80t


I am wondering if the red circle is the capacitor? It's next to the big fan in the bottom

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More photos

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I don't see anything here resembles a capacitor!

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I realized when I turned the temperature to 75F and I smelled electrical burning. If it's 71F and below, it seems to be OK. So for some reason, I guess the furnace overworked itself? Is it possible?


I also noticed small red LED light flashing fast 3 times and slow 3 times. I am sure there is something wrong electrically. The noise seems to come from the blower motor below and not the inducer motor on top.

  • 1
    Do you have a way to test the capacitor? Commented Jan 15, 2017 at 6:19
  • If I know how to test, I would. What tool do I need and what the capacitor looks like here? The furnace is very old and I can't find good instructions. I can take more pics..
    – HP.
    Commented Jan 15, 2017 at 6:24
  • The little metal stick is the flame sensor. It senses the flame, and tells the furnace that it's okay to continue to supply gas to the burners.
    – Tester101
    Commented Jan 15, 2017 at 13:52
  • What's the make and model of the furnace (should be on the label inside the cabinet, just below the burners)?
    – Tester101
    Commented Jan 15, 2017 at 13:55
  • 1
    Well I called someone and turned out the motor was bad as I suspected. Both motor and capacitor were replaced and it works perfectly now.
    – HP.
    Commented Feb 5, 2017 at 5:46

2 Answers 2


The filter placement looks incorrect to me. Every furnace I've seen has the filter on the other side of the venting into the fan box, causing the filter to be pulled tight against the opening. With the amount of air my furnace pulls, it would pull the filter away at the top and bottom allowing unfiltered air into the system.

My theory would be that the unfiltered air is allowing dust and lint into the heat exchanger and when it builds up enough it is burning off.

A quick image search should give a better visual of what I'm describing.

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  • The burn smell is definitely electrical and it comes when my wife cranked high temperature > 74F. Mine looks exactly like this checkthishouse.com/wp-content/uploads/…
    – HP.
    Commented Jan 20, 2017 at 5:39
  • @HP. I completely understand that burning electrical insulation has a particular pungent smell. But, in my experience, it is rare to smell burning electrical insulation and then not immediately see a much more egregious symptom, e.g. a motor stops spinning, a circuit breaker pops, etc. There are other things that smell like electrical insulation when burning so keep your search for an answer wide, don't limit yourself to looking exclusively for wires. Commented Jan 24, 2017 at 12:34

I called someone and turned out the motor was bad as I suspected. Both motor and capacitor were replaced and it works perfectly now

  • Please 'accept' your own answer.
    – Mazura
    Commented Nov 12, 2022 at 22:12

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