Quick answer
A certified electric heater with tip-over and overheat shut-offs, plugged straight into a wall outlet with a metre of clear space around it, is reasonably safe to run overnight in an occupied room. Extension cords, power bars, bedding and curtains are what turn one into a fire. Never run a fuel-burning heater, an oven or a barbecue indoors.
It is safe enough to run a space heater overnight if the heater is certified, has tip-over and overheat protection, plugs directly into a wall outlet, and sits with clear space around it in a room where someone is sleeping and would notice if something changed. It stops being safe the moment an extension cord, a duvet, a curtain or a fuel-burning heater joins the picture. The appliance is rarely the problem on its own — what it touches and what it is plugged into usually are.
The rules that make an overnight heater safe
- Check for a certification mark. Electrical products sold in Ontario must carry approval from a recognized body, and CSA or cULus are the marks you will usually see.
- Confirm it has both a tip-over switch and an overheat cut-out. Any current model should; something rescued from the back of the garage may not.
- Plug it straight into a wall receptacle. No extension cords, no power bars, no cube taps and no plug-in timers — those connections are not built for a continuous 1,500-watt load, and they are where melting starts.
- Give it a metre of clearance in every direction: bedding, curtains, upholstery, drying laundry, paper, the dog's bed.
- Set it on a hard, level surface where nobody can knock it over getting up in the dark.
- Keep it out of bathrooms and away from sinks unless it is specifically rated for damp locations.
- Do not leave one running unattended in a child's room or an empty room.
- Never run an unvented propane, kerosene or catalytic heater indoors, and never heat with the oven or a barbecue. Those put carbon monoxide into your living space.
Watch the circuit, not just the heater
A 1,500-watt heater draws about 12.5 amps. A standard 15-amp household branch circuit is rated for a continuous load of roughly 12 amps, so one heater is effectively the entire circuit — and in a 1970s or 1980s subdivision that single circuit may serve the bedrooms, the hall and a bathroom. Two heaters on the same circuit means a tripped breaker on a good night.
Older wiring deserves more caution. Houses wired with aluminum branch circuits in the late 1960s and early 1970s are prone to loose, overheating connections at devices, and pre-war homes in Westdale, Kerr Village and Old Oakville can still have knob-and-tube in sections. Neither is a good place to park a continuous 1,500-watt load. If a plug or receptacle is warm to the touch, discoloured, or the cord warms along its length, unplug the heater and have an electrician look at that circuit before you use it again.
What it costs to run, and when it stops making sense
A 1,500-watt heater uses 1.5 kilowatt-hours for every hour it runs flat out, so roughly 12 kilowatt-hours across an eight-hour night — enough to show up plainly on a Burlington Hydro or Alectra bill by month's end. Overnight is at least the cheapest window: Ontario's time-of-use pricing puts those hours in the lowest band, and the optional Ultra-Low Overnight plan is cheaper again between 11 p.m. and 7 a.m. Check which plan your utility has you on before you assume.
If one room needs a heater every single night, the heater is a symptom rather than a solution. That is a distribution or insulation problem — a starved duct run, a missing return, an uninsulated bonus room over a garage — and it has a permanent fix. Why one room is always cold covers the usual causes, and where ducts will never serve a room properly, a single-zone ductless mini-split at $4,000–$7,000 installed gives that room heating and cooling on its own thermostat.
Which type is best for overnight use
- Oil-filled radiator: no exposed element, no fan noise, and it holds warmth after it cycles off. The steadiest choice for a bedroom.
- Ceramic fan-forced: heats a room fastest, but combines a hot element with a moving fan, and it is the type most often dragged around by its cord.
- Infrared or quartz: warms objects and people in its line of sight rather than the room. Good to sit beside, less useful for holding a room through the night.
- Convector panels: quiet and even, though they are tall and easy to drape something over.
- Anything that burns fuel: not indoors, ever, whatever the box says about being ventless.
Space heater questions we get in January
- Can I run one all night in a nursery? We would not. Warm the room before bedtime and then take the heater out; a small child's room should not have a hot surface and a live cord in it overnight.
- Is the built-in thermostat enough to leave it unattended? It stops the heater from cooking the room. It does nothing about the cord, the receptacle or whatever falls onto the grille.
- Can I use one instead of the furnace to save money? Electric resistance heat costs more per unit of heat than natural gas in Ontario, so heating a whole house this way is usually the expensive route, and it loads circuits never designed for it.
- The breaker keeps tripping. Move the heater to a different circuit and run nothing else on it. If it still trips, that is an electrician's call rather than a heater fault.
- My furnace is down for a few days — can space heaters carry us? For a night or two, in one or two rooms, with the plumbing protected. Past that, get the heat repaired.
Space heaters are a bridge, not a heating system. If yours has become permanent equipment in one room, that is worth a proper look at airflow, duct sizing and whether the house is being heated the way it was designed to be. ZK Mechanical covers heating service and installation throughout Burlington, Oakville, Hamilton and the GTA with free quotes and written pricing — get in touch and we will come and measure rather than guess.