The three winter changes that return the most in a Canadian house are a real overnight thermostat setback, a filter changed on schedule, and sealing the duct runs that cross an unheated garage or attic. Everything else on the usual list is worth doing, but those three move the gas bill first. Below they are ranked by return rather than by how often you see them repeated.
The 10 tips, ranked by what they return
- Set the thermostat back overnight and while the house is empty. A programmable or smart control does it without anyone remembering.
- Change the filter every one to three months through the heating season, and check it monthly if there are pets or a renovation underway.
- Seal and insulate duct runs in unheated spaces — a garage ceiling, an attic, a crawl space — with foil tape and duct mastic, never cloth duct tape.
- Book the annual furnace service in the fall. A standalone tune-up runs $120–$250 in the GTA and catches the faults that turn into January call-outs.
- Get the humidity right. Air at 30% to 35% relative humidity feels warmer than dry air at the same temperature, which lets you hold a lower setpoint.
- Weatherstrip the doors and caulk around window frames and outlets on exterior walls, where the draughts you feel at ankle height come from.
- Top up attic insulation. Heat leaves through the ceiling first, and in older Ontario houses the attic is usually the thinnest part of the envelope.
- Open south-facing curtains during the day and close them at dusk, so the house takes free solar gain and then keeps it.
- Reverse the ceiling fans to clockwise on the lowest speed, but only in rooms with high ceilings where warm air genuinely stratifies.
- Replace a mid-efficiency furnace that is 15 or more years old. This one costs money, and it is the only item on the list that changes the ceiling on all the others.
Filters: the cheapest lever, and the easiest to get wrong
A filter that is packed solid restricts airflow across the heat exchanger, which trips the high-limit switch and shuts the burner down before the house is warm. That short-cycling burns more gas, not less, and wears the igniter. Hold the filter to a light: if you cannot see the bulb through it, it is finished.
The other half of the mistake is buying too much filter. A MERV 13 cartridge dropped into a 25 mm slot on a system designed for a MERV 8 raises static pressure across the blower and starves the furnace of return air. Match the filter to the cabinet rather than to the marketing on the box — the sizing and interval are covered in how often to change a furnace filter.
Duct sealing deserves a note of its own, because the material matters. Cloth duct tape dries out and lets go within a couple of winters, which is why the trade uses foil tape and brush-applied mastic instead. The joints worth sealing first are the ones you can reach: where branch runs leave the trunk, the seams on the return drop, and the boot connections under the floor of a room that never gets warm.
Thermostat setbacks that work in a Canadian winter
A setback saves because the house loses heat more slowly when it is closer to the outdoor temperature. The longer the setback runs, the more it returns — which is why the overnight block and the empty-house block matter far more than nudging the dial down while you are sitting in the room.
- Awake and home: whatever temperature you are comfortable at, held steady rather than chased up and down
- Asleep: two to three degrees lower, started half an hour before bed
- Empty house, eight hours or more: the same setback or deeper, with a recovery scheduled to finish before anyone gets home
- Away for a week: no lower than 15 °C, so the plumbing on exterior walls never gets close to freezing
- Never: turning the heat off entirely in a Canadian winter, which risks pipes and forces a long recovery
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One correction worth making: setting the thermostat to 26 °C does not heat the house faster. A single-stage furnace has one output, so the only thing a higher setpoint changes is how long it runs past the point you wanted. A smart thermostat installed with new equipment currently qualifies for $75 under the Home Renovation Savings Program — see the Ontario rebates page for what else is live.
Humidity: the comfort trick that lets you drop a degree
Winter air in southern Ontario is dry once it is heated, and dry air pulls moisture off your skin, which reads as cold. Bringing the house to 30% to 35% relative humidity usually lets a household sit comfortably a degree lower than it did before, and a degree held all season is real money.
The limit is condensation. Push humidity too high when it is -15 °C outside and the moisture lands on the coldest surfaces in the house — window glass, aluminium frames, the sills below them — where it rots wood and grows mould. Drop the setting as the temperature drops. A furnace-mounted humidifier needs a new evaporator pad each fall, about $20–$40, and a damper flip at each season change; whether you need one at all depends on the house.
Three popular tips that save nothing
- Closing vents in unused rooms. On a single-zone forced-air system this raises static pressure across the blower, pushes air out through duct leaks instead, and can drive the furnace into short cycling. If one room is always cold, the fix is balancing, not closing — see why one room stays colder than the rest.
- Running the furnace fan on continuous through the whole winter. It evens temperatures out, but it also adds a constant electrical draw, and on an older PSC blower that draw is not small.
- Sealing every draught in an older house without a thought for combustion air. A gas furnace and a gas water heater need air to burn; tightening a house right up around them is how backdrafting starts.
What to do this month
If it is autumn, book the service visit and change the filter the same week. If it is January and the bill has already landed, start with the setback schedule and the humidity setting, because both are free and take an evening. Leave the insulation and the equipment decisions for spring, when contractors have time and prices are not being set by a queue.
ZK Mechanical services heating systems across the GTA and Hamilton and runs maintenance plans that bundle the fall furnace visit with the spring air-conditioner visit. If your bills look wrong for the size of your house, book a look — sometimes it is the equipment, and often it is the ductwork nobody has opened in 20 years.
Frequently asked questions
What temperature should I set my thermostat to in winter in Ontario?
Set it to whatever you are genuinely comfortable at while awake, then let a schedule take two to three degrees off overnight and while the house is empty. The saving comes from the length of the setback, not its depth, so an eight-hour block matters far more than a deep dip for an hour. If the house will be empty for a week, do not go below 15 °C — pipes in exterior walls are the limit.
Does closing vents in unused rooms save money?
No. A forced-air system is designed around a fixed volume of air moving through it, and closing registers raises static pressure across the blower rather than reducing what the furnace burns. The air finds duct leaks instead, and the furnace can start tripping its high-limit switch. Balancing the dampers on the trunk lines is the real fix for uneven rooms.
How much does a furnace tune-up cost in the GTA?
A standalone furnace tune-up runs $120–$250 from a licensed GTA contractor and takes 45 to 90 minutes. It should include cleaning the burners, polishing or replacing the flame sensor, checking the inducer and blower, flushing the condensate trap on a condensing unit, and a combustion analysis at the flue. A maintenance plan bundles it with the spring air-conditioner visit for close to the price of booking both separately.
Is it cheaper to leave the heat at one temperature all day?
No, and this is the most persistent winter heating myth. A house loses heat in proportion to the difference between inside and outside, so a cooler house loses less. The extra energy used during recovery is smaller than what the setback saved, provided the setback runs several hours. The exception is a heat pump, where a deep setback can force expensive backup heat during recovery.