The first cold night of the season in the Valley usually comes with a familiar smell: the heater kicks on for the first time in months and the house smells a little like something is burning. Most of the time that’s normal. Sometimes it isn’t. Here’s how to tell the difference, and what to do if you’re not sure.
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The normal smell: dust burning off
Furnaces and heat pumps sit idle from spring to fall, and a thin layer of dust settles on the burners, heat exchanger or electric heat strips. When the system fires up, that dust burns off. It smells dry and dusty, a bit like a hair dryer or a toaster. It should fade within the first hour or so and be gone after the first day or two of use.
To help it clear faster, open a couple of windows for a few minutes and make sure you’ve put in a clean air filter. A dirty filter can keep the smell going longer and makes the system work harder.
Smells that mean turn it off
- Rotten eggs or sulfur. That’s the odor added to natural gas. Don’t touch the thermostat or any switches. Leave the house and call SoCalGas at 1-800-427-2200 or 911 from outside.
- Hot electrical or melting plastic. A sharp, chemical smell can mean an overheating motor, wiring or electrical part. Turn the system off at the thermostat and at its switch or breaker, and have it checked.
- A burning smell that doesn’t fade after a few hours, or that comes back every time the heat runs.
- Smoke coming from vents or the furnace itself. Turn it off and call 911 if there’s any sign of fire.
Carbon monoxide: the danger you can’t smell
A gas furnace burns fuel, and a cracked heat exchanger or a blocked vent can let carbon monoxide (CO) into the house. CO has no smell at all, so the dust smell tells you nothing about it. Early symptoms feel like the flu: headache, dizziness, nausea and feeling tired, often better when you leave the house.
- California requires CO alarms in homes that have gas appliances, a fireplace or an attached garage. Test yours when you first turn on the heat, and replace batteries as needed.
- If a CO alarm sounds, get everyone outside into fresh air and call 911.
- Don’t block the furnace’s air supply or vent pipe with stored boxes, especially in garage and closet installs common in Valley homes.
When to call for service
Call a licensed HVAC contractor if the smell lasts more than a day, if the furnace makes new banging, squealing or rumbling noises, if the burner flame looks yellow instead of mostly blue, or if the system keeps turning on and off. A yearly inspection before winter is the best time to catch problems like a cracked heat exchanger. See our heater checklist, what a maintenance visit includes, and common furnace problems.
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