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.