Space Heaters: The Real Cost Per Hour, and the Safety Rules That Are Not Optional
A space heater can be the cheapest heat in the house or the most expensive — the hardware is identical either way. The difference is entirely in how it is used: warming one occupied room while the rest of the house coasts at a lower temperature can save money; adding a heater on top of a house already heated to comfort just adds a second bill. This guide does the cost math with a formula you can run against your own hydro bill, then covers the safety rules, because space heaters are unforgiving equipment and the rules are the price of using one at all. General information only — follow your heater's manufacturer instructions above anything here.
The formula, and what a 1,500-watt heater actually costs
Electricity is billed in kilowatt-hours. The operating cost of any electric heater is: watts ÷ 1,000 × hours of heating × price per kWh (The Best Stuff cost guide, checked 2026-10-14). A 1,500-watt heater — the standard full-size portable — therefore uses 1.5 kWh for every hour its element is fully on.
| Setting | 1 hour | 4 hours/day | 30 days at 4 hrs/day |
|---|---|---|---|
| 1,500 W | $0.30 | $1.20 | $36.00 |
| 900 W (low) | $0.18 | $0.72 | $21.60 |
Illustrative rate: $0.20 per kWh, continuous full-power running, no thermostat cycling (table as published by The Best Stuff, checked 2026-10-14). Your real numbers will differ in three ways. First, your rate: use the marginal rate on your own bill, including variable delivery charges and taxes, and with time-of-use pricing use the rate for the hours you actually run the heater — an evening peak period changes the answer substantially. Second, cycling: a heater with a thermostat does not draw full power continuously once the room is at temperature, so real consumption is usually below the table. Third, the comparison that matters: the table is only half the ledger. The other half is what the central system didn't burn because you lowered its setpoint.
When a space heater saves — and when it cannot
It can save when: one room is occupied for hours — a home office, a workshop — and the central thermostat is genuinely turned down for the rest of the house. You are substituting 1.5 kW aimed at one room for a furnace heating every room. It cannot save when: the central thermostat stays where it was. Then the heater is pure addition. Canadian homeowner guidance makes the same point from the fuel side: in Ontario, electric resistance heat costs more per unit of warmth than natural gas, so heating the whole home with space heaters raises bills (Barrie Heating & Cooling). Notice that no heater design escapes this arithmetic — every electric resistance heater converts electricity to heat at essentially 100% efficiency at the outlet, so a premium model does not produce cheaper heat than a basic one. What better models buy is controls, safety features, and durability, not a discount on physics.
The safety rules (non-negotiable)
- Three feet of clear space, all around. Keep combustible materials — furniture, bedding, papers, clothing, curtains — at least 3 feet (0.9 m) from the front of the heater, and keep the sides and rear clear as well (manufacturer instructions, Home Depot-hosted manual; Air Conditioner Lab buying guide).
- Wall outlet only, never an extension cord. Plug directly into a wall receptacle with a circuit that can handle the draw; do not run the cord under rugs, carpet, or doors, where damage hides (Air Conditioner Lab; UL 1278 guidance summary).
- Buy and keep the safety features. Choose a heater bearing a recognised testing-lab seal, with a thermostat, overheat protection, and tip-over shutoff (UL 1278-conforming heaters include thermostat and tip-over or overheat protection).
- Never leave it running unattended. Turn it off when you leave the room or go to sleep. Heaters are for occupied, awake spaces.
- Floor only, flat and stable. Not on furniture, not near water or damp locations, and never used as a drying rack for gloves and towels — draped fabric restricts airflow and can ignite (safety guidance summarised from UL-based institutional rules; senior-home safety guide).
- Inspect before the season. Check the cord and plug for damage and never operate a heater with a damaged cord. Keep cords out of foot traffic so the heater cannot be tripped into its surroundings.
What success looks like: the heater sits on the floor with a visible 3-foot clear zone, plugged straight into the wall, warming the one room in use — while the central thermostat sits a few degrees lower than it used to, and the month's bill shows the substitution actually happened.
A worked decision, start to finish
Home office, weekdays, roughly 8 hours. The question: run a 1,500 W heater on its 900 W low setting with thermostat cycling, and drop the whole-house setpoint by 3°C during work hours — or heat the whole house to office comfort all day? Step one: cost the heater from your bill's marginal rate, not a national average. Step two: be honest about the setpoint — if the household will not actually accept a cooler house, there is no offset and the heater loses. Step three: run it for one billing cycle and compare against the same month last year, weather-adjusted by eye: a colder month should cost more, a similar month should cost less. That one-cycle test, with your own numbers, settles a question that no buying guide can settle for you. If the numbers come out even, keep the heater for spot comfort and drop the savings claim — comfort at no extra cost is still a fine outcome.
Choosing a heater: what the extra money should buy
Since every electric resistance heater converts power to heat at the same efficiency, the purchase decision is about controls and safeguards, not heat output per watt. Pay for: a thermostat that holds a set temperature and cycles the element (the feature that brings real consumption below the full-power table); tip-over and overheat shutoffs, verified on the unit's listing rather than the box copy; a cool-touch housing where children or pets share the room; and, for a bedroom-adjacent space, a genuinely quiet fan or a fan-free design so the heater is used rather than abandoned. Published buying guidance adds one more screening rule: only buy units carrying a recognised testing-lab seal, and prefer models whose protection features are part of a listed standard such as UL 1278 rather than marketing claims (Air Conditioner Lab; UL 1278 guidance summary). Skip paying premiums for "energy-saving" language attached to resistance heat itself — the saving features are the thermostat and the timer, and they save by switching the heater off sooner, not by making its watts warmer.
FAQ
Are infrared heaters cheaper to run? At the same wattage, no — the formula does not care about the heating style. Infrared units feel warmer faster because they heat occupants and surfaces directly, which can mean shorter runtimes, but a watt is a watt.
Can a space heater trip my breaker? Yes: 1,500 W is a heavy single load. If a circuit is shared with other large appliances, tripping is the circuit protecting itself — move the heater to a less loaded circuit rather than working around it (Air Conditioner Lab).
Is it safe to run one overnight in a bedroom? The standing guidance is no unattended operation. Warm the room before bed, then switch it off; bedding near a heater is exactly the scenario the 3-foot rule exists for.