A small space heater is sized in watts, and Ontario’s Save on Energy puts the rule at about 10 watts per square foot. That makes 1,500 watts a match for roughly 150 square feet.
It is also the ceiling. A standard residential wall plug will not safely supply more than 1,500 watts.
Same watts, same heat, on every model sold
Natural Resources Canada is blunt about this. Electric space heaters “produce one unit of heat for every unit of electricity,” making them 100 percent efficient at the end use.
Two heaters rated alike use the same energy and deliver the same heat. That is why space heaters carry no ENERGY STAR certification at all.
NRCan also places them outside Canada’s Energy Efficiency Regulations, apart from a rule covering electric boilers. There is no efficiency rating to shop on.
The only real efficiency jump in home heating is a heat pump. A geothermal unit moves three units of heat per unit of electricity, or 300 percent.
Where 10 watts per square foot stops working
The rule scales cleanly until it hits the plug. A 300-square-foot living room implies 3,000 watts, which means two circuits rather than one appliance.
Personal desk heaters run about half the wattage of a whole-room unit, which is the right call if you only need one chair warm.
The rule also ignores ceiling height, insulation and exterior walls, so treat it as a starting point. Our roundup of the best portable heaters for Canadian winters shows what those wattage figures look like across real models.
What an hour of 1,500 watts actually costs
Running 1,500 watts for an hour consumes 1.5 kWh. The Ontario Energy Board’s prices, set for November 1, 2025, turn that into money.
On the Tiered plan at 12.0 cents per kWh, an hour costs 18.0 cents. On Ultra-Low Overnight it costs 5.9 cents overnight and 58.7 cents during the weekday 4 p.m. to 9 p.m. peak.
That is a tenfold swing on identical hardware, decided by the clock alone. The peak ULO price is 39.1 cents per kWh, nearly four times the off-peak rate on the same plan.
Eight hours a day for a month is 360 kWh, about $43 at the Tier 1 rate. Those are supply rates only, so delivery lands on top.
That much heating can also push a household past the 1,000 kWh winter tier threshold into the higher rate. An energy-monitoring smart plug shows the real draw instead of the box claim.
Four heater types, four real trade-offs
Fan-forced convection warms a room fastest, but it pushes dust and allergens around and it is the noisiest option. Radiant and infrared models heat you rather than the air, suit a fixed workspace, and cost more.
Oil-filled units hold heat after shutoff, paid for with a slow warm-up and more bulk. Micathermic panels drop the fan and mix radiant heat with convection.
Save on Energy is clear that a heater only lowers a bill if you turn the heat down elsewhere. A smart thermostat that drops the whole-house setpoint is what makes zone heating pay.
The safety rules that are not negotiable
Check the label for CSA or UL certification, and pick a model with tip-over and overheat shutoff.
Plug the heater straight into the wall. Power bars and extension cords are not built for that current, and a cord run under a rug is its own fire risk.
The National Fire Protection Association keeps a three-foot clearance around all heating equipment. Its January 2026 release counted 37,365 US home heating fires a year across 2020 to 2024, with space heaters and heating stoves behind 73 percent of the deaths.
Frequently asked questions
How many watts do I need for a 200-square-foot room?
At 10 watts per square foot that is 2,000 watts, more than one outlet can supply. You would need two heaters on separate circuits, or a hardwired unit.
Is an expensive small space heater cheaper to run?
No. At equal wattage the running cost is identical, so the premium buys controls, build and comfort features, never efficiency.
Does a thermostat on the heater save electricity?
Yes. The element cycles off once the room hits the setpoint instead of running flat out. A timer with auto shutoff does the same for rooms you leave.
Vicki Lewandowski covers apps, consumer gadgets, and step-by-step digital how-tos for 3Zebras, with a focus on clear instructions that help readers fix problems and get more out of the devices they already own.