Quick answer
A house in an Ontario winter gets uncomfortable in a few hours without heat, but pipes take longer. An insulated home near freezing outside usually has a day or more before pipes in exterior walls are at risk; a drafty older house at -20 °C can get there overnight. People come first: move infants, seniors and anyone unwell before the rooms drop below 16 °C.
How long a house can go without heat in an Ontario winter depends on three things you can check: the outdoor temperature, how well the house holds heat, and who lives in it. Comfort goes first, in hours. Health comes next, and for a baby or an elderly parent that limit arrives long before any pipe is in danger. Plumbing is last, and it is the one that costs money.
The timeline by house type and outdoor temperature
Use the thermostat reading, not the clock. No two houses cool at the same rate, but the order is predictable, and these are the patterns behind most no-heat calls.
- 2000s and newer builds, around 0 °C outside: slow. Tight construction and full insulation hold heat, and there is often a day or more before pipes in outside walls are at risk.
- 1970s to 1990s subdivision homes, around -10 °C: a noticeable drop by evening and a cold house by the next morning. Rooms over the garage and bathrooms on outside walls lead the way.
- 1950s and 60s bungalows and pre-war brick houses, at -20 °C with wind: fast. Uninsulated walls and leaky windows can take the main floor into single digits overnight.
- Century farmhouses and anything on a crawlspace: fastest. Pipes under the floor can freeze while the kitchen above still feels tolerable.
Wind matters as much as temperature. A calm -15 °C night is easier on a house than a -8 °C night with a gale off Lake Ontario or across the open fields above the Niagara Escarpment, because wind drives cold air through every gap.
People before pipes: the health threshold comes first
Decide about people first. The World Health Organization's housing guidance treats 18 °C as the minimum indoor temperature for health in cold seasons, and infants, seniors and anyone with a heart or lung condition feel a cold house soonest. If the rooms are heading below 16 °C and no repair is confirmed for that day, move those family members to a relative's, a neighbour's or a hotel. Healthy adults in layers can manage a cold house for a night; they should not make that choice for a newborn.
Hour by hour: what to do while the heat is out
- First hour: check the thermostat, furnace switch, breaker and filter, then book the repair. What to do when the heat stops working at night lists the quick checks.
- Hours one to four: close off unused rooms, draw the curtains, and gather the household in one or two rooms with electric space heaters on separate circuits.
- Once the house is below 15 °C: open the cabinet doors under kitchen and bathroom sinks on exterior walls so room air reaches the pipes.
- Once the house is near 10 °C, or the night will be below -10 °C: run a pencil-thin trickle at the taps farthest from the water meter.
- If you are leaving, or the house is headed below 5 °C: shut the main water valve, open the taps on every level to drain the lines, and flush the toilets.
Do not improvise heat with the oven, a barbecue or a propane heater, which put carbon monoxide into a closed house. The safe and unsafe options are compared in can I use my oven to heat my house. Homes with boilers and radiators have water in the heating system itself and need extra care, covered in what to do if heating pipes or radiators freeze.
Rural properties have one more wrinkle. On a private well in Kilbride, Carlisle or rural Caledon, a power outage that stops the furnace also stops the well pump, so the trickle trick only lasts as long as the pressure tank. Drain the lines sooner.
Tenants: Ontario's 20 °C minimum heat standard
If you rent, the landlord's duty has a number on it. Regulations under Ontario's Residential Tenancies Act treat heat as a vital service from September 1 to June 15 and require at least 20 °C in the unit, and municipal property-standards bylaws can set their own dates and temperatures. Report the outage in writing right away, and keep a note of the indoor temperature and the time. Details are in what temperature a landlord must keep a rental in Ontario.
What it costs to get the heat back on
Most no-heat calls end with a repair, not a new furnace.
- Diagnostic visit: $90–$150, credited toward the repair.
- Common fixes such as a flame sensor, igniter or capacitor: $150–$450.
- Draft inducer motor: $400–$900.
- Blower motor: $500–$1,500, depending on the motor type.
- Control board: $500–$1,200.
Compare those numbers with a burst pipe and a soaked ceiling and the decision to call early makes itself. ZK Mechanical's emergency service line, (647) 801-1252, is answered 24/7 with no overtime, weekend or holiday surcharge, and covers Burlington, Oakville, Milton, Hamilton, Mississauga, Brampton and west Toronto. If the house is holding temperature and the repair can wait for morning, book through the contact page.