Q&A / 

Furnace Smells When Turned On

Quick Column Summary:

  • Is furnace smell dangerous
  • Carbon monoxide is odorless/dangerous
  • Dust accumulation causes smell
  • Clean furnace and ductwork

Jane, who lives with an old octopus gravity-feed (probably) furnace in Roseville, MI, has an odor issue. Let her describe it:

"We moved into a home that has an old octopus furnace - it is labeled Sunbeam No. D - 522.

There is a horrible smell when we turn it on. We don't think it's carbon monoxide because our detectors are ok - no signal or alarm.

The furnace is probably 60 or more years old.

Is the smell dangerous? My husband is disabled and when the weather is as cold as it has been  we need to turn on the heat."

Here's my response to Jane:

Jane, first carbon monoxide is colorless and ODORLESS. That's why it's so dangerous. When it's in a house or confined space you can't smell it.

You didn't give me one other piece of data that I need to make a conclusive decision for you, so I'm going to guess.

I'm going to assume this odor happens only when the furnace comes on for being off for weeks or months.

This is VERY NORMAL. The odor you're smelling is dust that accumulates on the heat exchanger and inside the furnace near the heat exchanger.

The hot temperatures there actually burn up the dust and you're smelling the smoke, even though you can't see it.

This happens even at lower temperatures farther down the ductwork and even on hot-water radiators like I have in my own home.

Now, if the odor happens EVERY TIME the furnace operates, then you have something objectionable in the ductwork. 

What that might be I have no clue. You'll have to investigate.


4 Responses to Furnace Smells When Turned On

  1. Thanks so much for your answer. As you guessed, we had not used the furnace in a few months. The temperature has fallen drastically in the last few days so we needed to turn it on it at night. If the problem continues every time we use it, we will take your suggestion and have the ductwork looked at. Thanks again!!

  2. This happens to me every fall when I first turn on my furnace.....I think it must happen to everyone.....
    This is way too early to have to turn it on, but I have it on today just to break the chill (as they say) then I will turn it off.....had it on a couple of times last week too.....time to put the fleece sheets back on the bed.....BTW does anyone know where you can find GOOD Tee Shirt Shirts....or Jersey for another name ? I purchased some from QVC and they were the best ever...(they do not sell them anymore 🙁 I have been to every store near me and a 100 miles away and still can't find them.....your help will be appreciated if anyone knows.....thanks.....
    Wonderful sheets Tim, they snug your bed, no wrinkles at all when you sleep on them.....now if you start selling them, I will be your best customer :).....just sayin...............

  3. Bought a 15 year old condo in CA in 1995. Had bad odors when I checked the furnace. Then later when I needed it at night for heat or days for A/C. I pulled off one of the supply registers and saw all kinds of construction debris and dirt.
    Had a firm in to clean the ducting. They treated the debris as hazardous materials. They suspected mold was in the ducting. When they were through, odors were gone and never reappeared in the 9 years that I owned the place. I changed the air filters with good quality filters regularly.

  4. We are renting a house built in the 1930s with a Payne gravity furnace, which has been converted into an upstairs-downstairs duplex. We don't need heat for most of the year, but when we do, we run it pretty consistently. For the last 3 years, there has been a terrible melting rubber smell that gets increasingly worse with use. It comes up even if our downstairs neighbor is the only one using the heat. This is definitely not just dust that needs to burn off, but our landlord insists the best way to fix the problem is to crank the heat until the smell goes away. I am concerned it's mold or something worse and don't want him turning on the heat and potentially poisoning us. We can't see anything when we shine a light down the vents. The furnace is completely blocked in and everything is coated in asbestos. Any suggestions on what the problem is or how we could fix it?

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