That Burning Smell When the Heat First Comes On

The first cold night of October, the heat comes on, and the house fills with a burning smell. Usually it is dust and it is gone in twenty minutes. Sometimes it is not, and the difference is worth knowing before you decide whether to go back to bed.

A burning smell when the heat turns on is usually dust

Dust settles on the heat exchanger over a summer of sitting idle. The first time the burners run, it burns off. The smell is dry and dusty, it appears within a minute of the system starting, it is strongest at the registers, and it fades steadily over the first few cycles.

If that describes what you are smelling, open a couple of windows for a few minutes and let it clear. If it is still there on the third or fourth day of running, it is not seasonal dust and it wants looking at.

The ones that mean stop

Electrical. Sharp, acrid, like hot plastic or ozone rather than dust. That is insulation on wiring, a motor winding, or a connection overheating. Shut the system off at the switch and do not run it again until someone has looked at it.

Burning plastic or rubber. Something is in contact with a hot surface, or a belt or bearing is failing. Same response: off, then call.

Any smell of gas. Rotten eggs or sulphur is the odourant added to natural gas. Do not investigate it, do not flip switches, and do not use anything electrical. Get everyone out of the house, then call the gas utility from outside. That call comes before ours.

The smell that is not a smell

Carbon monoxide has no odour at all. That is precisely why it kills people, and why a burning-smell article has to mention it: the smells you can detect are not a reliable guide to whether combustion is safe.

Every home with fuel-burning equipment needs working carbon monoxide alarms, on every level and near sleeping areas, tested at the start of each heating season. If an alarm sounds, treat it as real, get outside, and call from there. Headaches, nausea or drowsiness that improve when you leave the house and return when you come back are a reason to act on the same night.

Why October is when this happens

Nothing about the equipment changes overnight. What changes is that a system which has been sitting for six months runs hard for the first time, and any fault that developed quietly over the summer surfaces at once — usually at eleven at night, on the first genuinely cold evening, when everyone in the county has just turned their heat on.

That is the argument for a heating maintenance visit in September rather than a repair call in October. A technician firing the system under controlled conditions finds the same faults, on a weekday, with parts available.

What we check on a burning-smell call

Combustion analysis at the flue, so the numbers say what the burner is doing rather than a guess. A heat exchanger inspection, because a crack is the fault with the most serious consequences and the one you cannot see from outside the cabinet. Amp draw on the motors and a look at every electrical connection. Then the ordinary things: filter, blower wheel, and whether anything flammable has been stored against the equipment.

If it turns out to be dust, you will be told it was dust. If it is not, our emergency service runs around the clock.