Burning smell when the heat comes on
The first time you turn the heat on each fall, a burning-dust smell is common. Dust settles on the heat exchanger or heating elements over the summer and burns off, and the smell should fade within an hour or so. A smell that lingers, or one that smells like hot plastic, oil or rotten eggs, is different and needs attention. Swapping the filter before that first cold night cuts down on the smell and gives the furnace an easier start to the season.
Why heat smells at first
Furnaces, heat pumps with backup heat, and baseboard heaters all collect dust while they sit unused. When they heat up, the dust burns off and you smell it through the vents.
The type of smell tells you a lot. Dusty and fading is normal. Electrical or burning plastic that doesn't fade, oily or smoky, or rotten eggs each point to a problem.
Common causes of the smell
Normal the first few times each season.
The system runs hot.
Toys, paper or lint can scorch.
Motors or wiring can smell hot or like plastic.
| Smell | Likely cause | What to do |
|---|---|---|
| Dusty, fades within an hour or so | Dust burning off | Normal. Open a window. |
| Rotten eggs or sulfur | Gas leak | Get out; call from outside. |
| Burning plastic or electrical | Overheating part | Turn it off; call a tech. |
| Musty or moldy | Moisture in the ducts or system | Call a tech to check. |
Track down the smell
- Name the smellDusty or like a hair dryer is normal at first. Rotten eggs means gas; burning plastic or rubber, or a hot electrical smell, means something is overheating. Each needs a different response. Also check that nothing is touching a baseboard or space heater.
- Give it some timeFor a dusty smell, crack a window and let the heat run. It usually fades within an hour or so. If it's still strong after a few hours, go on to the next steps.
- Change the filterA clogged filter can make the system run hot and smell. Turn the furnace off at the thermostat first, then swap in a clean one with the arrow pointing toward the furnace.
- Vacuum the ventsPull off the floor and wall registers and vacuum the dust out of the openings. For baseboard heaters, turn off the breaker and let them cool, then vacuum the fins gently.
- Check the CO alarmMake sure you have a working carbon monoxide alarm near the bedrooms, and test it. It's the backstop for any fuel-burning heater.
Watch it done
- The dusty smell fades within an hour or so of running
- A clean filter is in with the arrow pointing the right way
- The CO alarm sounds when you test it
Smell lasting days, or like gas or burning plastic? Turn off the heat and call a pro.
If the smell won't go away
If the dusty smell hangs around for days, the ducts or the furnace may need cleaning. A yearly tune-up usually covers the furnace.
If a space heater or baseboard is the source, check that nothing is touching it and it's clean. Keep things at least 3 feet away from space heaters.
What a pro typically charges (a rough estimate; prices vary by area): An HVAC tune-up typically costs $80–$200. A service call for a burning smell usually runs $100–$300 before repairs.
Find an HVAC technician near you