Short answer: A dusty burning smell for the first few minutes of the season is usually normal. A smell like burning plastic or rubber, electrical burning, or rotten eggs is not. Turn the furnace off and call for help.
The first cold night of the year often brings a burning smell from the vents. Most of the time it is harmless dust, but some smells mean the furnace should be shut off right away.
Usually normal
- A dusty smell when the heat first runs after months off
- A light smell that fades within an hour
- A smell after a new filter is installed
Not normal
- Burning plastic or rubber, which can mean an overheating motor or wiring
- A sharp electrical smell
- A smell that does not fade after a few hours
- Smoke from the vents or the furnace cabinet
Rotten egg smell
Natural gas has an added smell like rotten eggs. If you smell it, do not switch anything on or off. Leave the house, then call the gas company or 911 from outside.
What to do
- Turn the thermostat off if the smell is not just dust
- Check and replace a dirty filter
- Make sure nothing is stored against the furnace or vents
- Check that carbon monoxide alarms are working
- Call an HVAC technician before running it again
When to call a professional
Call an HVAC technician for any smell that lasts, smells electrical or comes with noise, smoke or the furnace shutting off. A yearly tune up before winter catches most problems early.
Frequently asked questions
How long should the dust smell last?
Usually from a few minutes up to an hour on the first runs of the season.
Can a dirty filter cause a burning smell?
Yes. A clogged filter makes the furnace overheat. Replace it every one to three months.
Do I need a carbon monoxide alarm?
Yes, on every level and near sleeping areas if you have a gas furnace or attached garage.
Related
Read our furnace repair page and our carbon monoxide safety guide.
For more background, see the U.S. Consumer Product Safety Commission, and if you need help, Sifixit can connect you with a local provider.
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