Heater Smells Like Burning? What Is Normal and When to Call

The burning dust smell the first time you turn on the heat

A light, dusty burning smell the first few times the heat runs each season is usually normal. In San Antonio the heater can sit unused for most of the year. Dust settles on the furnace burners and heat exchanger, or on the electric heat strips of a heat pump. When they heat up again, that dust burns off.

• It smells like dust or a hot toaster, not like plastic, wiring or rotten eggs.
• It is strongest in the first minutes and fades over the first few heating cycles, usually within a few hours.
• No smoke comes from the vents, and no alarms go off.

If the smell is still there after a day of normal use, or it keeps coming back every time the heat starts, have the system checked.

Smells that are not normal

• Rotten eggs or sulfur: natural gas has an added odor that smells like rotten eggs. Leave the house, do not flip switches, and call your gas company from outside.
• Burning plastic, hot wiring or an electrical smell: this can point to an overheating blower motor, wiring or another electrical part. Turn the system off at the thermostat and call.
• Burning rubber: a slipping belt on some older blowers, or a motor working too hard.
• Smoky, sharp or exhaust-like smell: the furnace may not be venting properly, or the heat exchanger may be damaged. Read how to tell if your heat exchanger is cracked.
• Musty or moldy smell: not a burning smell, but common when the heat first comes on. It usually means moisture or dirt in the ducts or around the indoor coil. See duct cleaning and repair.

Carbon monoxide has no smell. A smell cannot tell you whether CO is present, so every home with a gas furnace should have working CO alarms.

Heat pumps and electric heat strips

Many San Antonio homes heat with a heat pump. On the coldest mornings, or in EM heat, the system turns on its electric heat strips. They collect dust just like a furnace, so the first time they run you may notice a short burning-dust smell. If the AUX or EM light is on, read EM heat vs. heat. A strong electrical smell, or a smell every time the strips run, should be checked. See heat pump repair.

What you can safely do yourself

• Change the air filter. A clogged filter makes the system run hot and can add to the smell.
• Open a window or two and let the system run through a few cycles if it is only a dusty smell.
• Look at the floor vents. A toy, dryer sheet or bit of plastic that fell into a register will smell when warm air hits it.
• Clear the furnace closet or attic platform. Boxes, paint cans, cleaning products and clothes should not be stored against the furnace.
• Test your smoke and CO alarms at the start of heating season.

Burners, gas valves, wiring and motors should be checked by a licensed technician. If the heater still blows cold air instead of warm, see heater blowing cold air.

When to turn it off and call

• You smell gas: leave the house and call your gas company from outside.
• A carbon monoxide alarm sounds: get everyone out and call 911.
• You see smoke from the vents or the unit, or smell burning plastic or wiring.
• The smell does not fade after a day, or comes back every time the heat starts.
• The breaker trips, or the furnace makes banging, squealing or grinding noises.

Cowboy's answers 24/7 with our own dispatch on Blanco Road. On every heating call we check gas safety before we call it fixed. See furnace repair, heating repair in San Antonio, or call (210) 495-7771.

Frequently asked questions

Why does my heater smell like burning when I first turn it on?

Dust settles on the furnace burners or heat strips while the heat is off for the season. When the heat runs again, that dust burns off. A light dusty smell that fades within a few hours is usually normal.

How long should a burning smell last after turning on the heat?

A normal burning-dust smell usually fades over the first few heating cycles, often within a few hours. If it lasts more than a day or returns every time the heat starts, have the system checked.

Is a burning smell from my furnace dangerous?

A dusty smell on the first cold day usually is not. A smell of burning plastic, wiring or rubber, smoke from the vents, or a rotten-egg smell is a reason to turn the system off and call.

What does a gas leak smell like?

Natural gas has an added odor that smells like rotten eggs or sulfur. If you smell it, leave the house, do not flip switches, and call your gas company from outside.

Can I smell carbon monoxide from my furnace?

No. Carbon monoxide has no smell, so a smell cannot tell you whether it is present. Keep working CO alarms in any home with gas appliances.

Related service: heating repair in San Antonio · furnace repair · heat pump repair. Cowboy's AC answers 24/7 at (210) 495-7771.