If there was a crack in a heat exchanger in a natural gas forced hot air furnace, would it trigger a Carbon Monoxide detector to go off?

This is NOT happening in my house. The reason why I am asking is I have been smelling smoke (combination of cigarette / wood burning) the past 3 days and I really only smell it when I am in the house. My wife can't smell it but she really does not have a good sense of smell.

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    CO does not have a smell to humans .... as a side note, maybe your wife smokes in secret
    – jsotola
    Dec 31, 2020 at 16:56
  • Agree on both points. But she is not in the house from 9-5 and that is when I am smelling it the most Dec 31, 2020 at 17:00
  • if you live in northern hemisphere, it could be a simple case of more wood smoke outside, since it is winter ... the smoke particles stick to your clothes, and you smell the smoke when you come inside
    – jsotola
    Dec 31, 2020 at 17:07
  • Fair point, took a couple of showers with soap that has strong odors, and new clothes, but still smell it. I dont really smell it outside either Dec 31, 2020 at 17:09
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    One thing I always advise to check is a furnace filter. If the filter is clogged it will cause the output temperature of the furnace to be higher and you can get weird smells. Also verify you don't have any electric heating devices like a plug in heater or heated baseboard. These often get dust covered and smell oddly when they turn on.
    – mfarver
    Dec 31, 2020 at 17:49

1 Answer 1


If the heat exchanger is leaking Carbon Monoxide into the heated air in dangerous quantities, it SHOULD trigger the Carbon Monoxide detector, but I wouldn't assume that everything is fine just because the alarm is silent. Your life is too important to gamble on that device working as intended.

On a side note, I think that a wood or cigarette burning smell is much different than any odors produced by a natural gas furnace (in my opinion anyway).

Best bet is to inspect your furnace periodically, or hire someone to do so.

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    Agreed, I check it at the the beginning and end of each season. I should also say that I bought a brand CO detector and put it in front of vents and no alarms. Dec 31, 2020 at 16:54

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