To get your furnace ready for the first cold night, switch the thermostat to heat on a mild day, before you need it, and check that warm air comes out. Before that test run, open and clear the registers, move stored things away from the furnace and test your CO alarms. A faint dusty smell on the first run is common. If the furnace doesn't start, you'll still have daylight and time to get help.
Safety first: If a CO alarm goes off, leave the home now and call 911 from outside. If you smell gas, leave and, from outside, call 911 and Enbridge Gas's emergency line at 1-866-763-5427. On propane, call 911 and your propane supplier. Don't stay to test the heat.
How do I get my furnace ready for the first cold night?
Do a short test run on a mild afternoon in October or early November, not on the first night below freezing. Work through a few simple checks first, then switch to heat and give it some time. A furnace that has sat since spring may show a problem only when it's asked to heat. Finding that out in daylight gives you room to book a visit before the house gets cold.
Before-the-cold checklist
- Thermostat set to heat, with fresh batteries if it uses them.
- Supply registers open, and returns not blocked by furniture or rugs.
- Storage, laundry and cleaning products moved away from the furnace.
- A clean filter in place.
- Nothing stacked against the furnace's outdoor vent pipes, such as bins, firewood or garden items.
- CO alarms tested with the test button.
For a full CO alarm check, see our carbon monoxide alarm checklist.
What should I check on the thermostat after summer?
Switch the mode from cool or off to heat, and set the temperature a few degrees above the room. Replace the batteries if the screen is dim or the thermostat uses them and you can't remember the last change. Check that a summer schedule, away mode or hold isn't still running. Then listen for the furnace to start within a few minutes.
Summer settings that often carry over
- Mode still on cool, or the system set to off
- A vacation or away mode from a summer trip
- A schedule built around air conditioning, with low heat settings or none
If the thermostat seems to be calling for heat and nothing happens, our guide to a thermostat that says heat but the furnace won't start walks through the signs in order.
Do my registers and air returns need to be open and clear?
Yes. A forced-air furnace moves house air in through the return grilles and back out through the supply registers. Natural Resources Canada advises keeping ducts, warm air registers and cold air returns clear so air can move through the system. Over the summer, furniture, rugs and boxes often end up on top of them, or registers get closed to push cool air elsewhere.
A quick walk-through
- Open each supply register, especially in rooms you closed off for summer.
- Pull couches, beds and rugs back from return grilles.
- Check that the curtains don't hang over floor registers.
- Note any room where you feel no airflow at all once the heat runs.
A room with no airflow is worth mentioning at your next service visit.
What should be cleared away from the furnace?
Anything stored around it. Furnace owner's manuals warn against keeping combustible materials, gasoline, paint, or other flammable liquids or vapours near the furnace. They also say not to cover it, stack things against it or use the furnace room as a closet for chemicals and cleaners. A furnace also needs air around it to burn fuel safely.
Move these away before the first run
- Boxes, laundry, holiday decorations and sports gear
- Gasoline, paint, thinners and other flammable liquids
- Bleach, pool chemicals and other cleaners
- Anything leaning on the furnace or its pipes
Leave the pipes, wiring and gas line alone. Just clear the space around them.
Is a burning smell normal the first time the heat comes on?
A faint, dusty burning smell on the first run of the season is common. Dust can settle on the furnace and in the ducts over the summer, and it usually burns off once the furnace heats up. Furnace makers' general homeowner guidance says the smell should fade fairly quickly. A strong smell, one that keeps coming back, smoke, or a plastic or electrical smell isn't normal.
Smells that mean stop
- Gas or rotten eggs: leave the home and call 911 and Enbridge from outside.
- Burning plastic, rubber or an electrical smell: turn the heat off at the thermostat and call.
- Smoke or haze from the registers: get everyone out and call 911.
- A dusty smell that doesn't fade, or returns every time the heat runs: turn the heat off and call.
Our guide to furnace gas and burning smells explains each smell in more detail.
What if the furnace doesn't start the first time I switch to heat?
Start with the thermostat: make sure it's set to heat, has power and is set above room temperature. If it is calling for heat and the furnace stays silent, or you hear it try to start and stop, the problem is in the furnace. Don't keep restarting it. Note what you see and hear, and call. That's the reason to test on a mild day.
Where to look next
- Furnace tries to light but stops: our guide to a furnace that won't ignite lists the safe checks.
- A flashing status light: take a photo of the pattern before you call.
- Nothing happens at all: check the thermostat guide linked above, then call.
If the weather is about to turn cold, call our 24/7 emergency furnace repair line at (249) 209-2216 rather than waiting for a booking.
When should I book a tune-up, and when should I call 24/7?
Book a tune-up when the furnace works but hasn't been checked in the past year. Ontario's carbon monoxide safety guidance says fuel-burning appliances, chimneys and vents should be cleaned and inspected by professionals every year before cold weather sets in. Call 24/7 when the furnace won't heat and a cold night is coming, or if there's a smell, water or a repeated shutdown.
Book a tune-up if
- The furnace started and heats, but it's been more than a year since its last service.
- It ran loudly, cycled oddly or struggled to keep up last winter.
- You've moved in and don't know when it was last serviced.
Call 24/7 if
- It won't start or won't stay on, and the temperature is dropping.
- Someone in the home is vulnerable to cold, such as an infant or older adult.
- There's a burning plastic or electrical smell, smoke, or water by the furnace.
Professional servicing is for the parts you shouldn't touch yourself. Natural Resources Canada's servicing list includes the combustion and vent systems, the heat exchanger and the safety controls.