It smells like something burning when the heat comes on

Usually harmless: the first cold morning

Around Bastrop the heat may sit unused from March to November; the median first freeze at the Smithville station arrives on November 19. Months of dust on heat strips or a burner give off a dry, dusty burning smell for the first few cycles. Opening a window and letting it run through usually clears it within an hour.

Not harmless: switch the heat off and call

• Hot plastic, rubber or an electrical smell. A blower motor overheating, a wire or connection burning, or a strip shorting against the cabinet.
• Smoke from a vent or the unit. Turn the system off at the thermostat and the breaker, and call 911 if there is visible smoke or fire.
• A smell that persists for hours, or returns every cycle.
• On a gas or propane furnace, a smell of gas. Leave the house and call 911 or the gas provider from outside.

What a technician checks

The blower motor's bearings and current draw, the heat strips and their terminals, the sequencer and limit switches, and the wiring in the cabinet for heat marks. On a gas or propane furnace, the burners, the flue and the heat exchanger, with combustion and carbon monoxide readings written down.

Reduce it next year

Change the filter before the first cold snap, and run the heat for twenty minutes on a cool October evening with a window open. That burns the dust off while nobody needs the heat, and shows up any fault while there is still a choice of appointment.

What to say when you call

• What the smell is like: dusty, plastic, rubber, electrical, gas
• How long it has lasted, and whether there was smoke
• Electric furnace, heat pump, gas or propane
• Whether a breaker tripped
• Your ZIP code and where the indoor unit sits

Common questions

Can I keep the heat on if the smell is fading? A dusty smell that fades within the first hour, yes. Anything else, turn it off until it is checked.

The smell comes with a tripped breaker. That combination points at a strip or a motor. Leave the breaker off; see the breaker page.