I noticed the smell while putting summer clothes into a storage bag. The furnace had just started for the first time that autumn. My first thought was 'probably dust'. My second was that probably was not a very useful safety check.
I stopped packing and checked what was actually happening from a safe distance. Was there visible smoke? A sharp electrical smell? A gas odour? An alarm? Those are different situations from a faint, brief smell when equipment first warms up.
Do not turn an emergency into an experiment
Source: Enbridge Gas Ontario: safety
If you smell gas, leave the building and call for emergency help from outside. Do not operate switches or use a phone inside. Smoke, fire or a carbon monoxide alarm also calls for getting everyone out and calling 911. A scented candle or an open window is not a diagnosis.
For a persistent or unfamiliar burning smell without an immediate emergency, stop using the equipment if you can do so safely and seek professional advice. There is no universal number of minutes that makes a burning smell acceptable.
The storage bag could wait
Source: Natural Resources Canada: heating and cooling maintenance
NRCan recommends regular professional checks of heating equipment and routine filter care according to the owner's instructions. I checked that our service was booked and that boxes had not migrated into the furnace's working space over summer. I did not remove panels to look for the source of a smell.
I also wrote down when it happened and whether it returned. A clear description would help the technician far more than my first conclusion.
The storage bag stayed in the bedroom that afternoon. It was a small interruption, but I preferred it to teaching myself to dismiss a new smell every time the heating came on.
