How to Choose a Space Heater: Types, Wattage, Safety

Short answer: For a bedroom you sleep in, buy an oil-filled radiator with a thermostat. For warming up a bathroom or office fast, buy a ceramic fan heater. For a drafty room where you sit in one spot, a radiant heater warms you without heating the whole space. Whatever you buy, make sure it has a tip-over switch and an overheat cut-out, and plug it straight into the wall.

The four types

Type	How it heats	Best for	Noise	Weak point
Ceramic fan	Blows air over a hot ceramic plate	Fast heat in a small room, bathrooms, offices	Fan noise	Dries the air; room cools fast when it stops
Oil-filled radiator	Heats oil inside sealed fins, warms the room slowly	Bedrooms, all-night use, steady warmth	Silent	Slow to start; heavy
Radiant (infrared or quartz)	Warms objects and people in its line of sight	A chair or desk in a cold room, garages, patios	Silent	Does little for the air; a glowing element
Convection panel	Warms air that rises past a panel	Even background heat in a closed room	Silent	Slow; needs a closed door

Step 1: Pick the type for the job

You want the room warm in five minutes. Ceramic fan heater. It is the fastest and the cheapest to buy, and it is fine for a bathroom before a shower or a home office in the morning. It is also the loudest, and the room cools down almost as fast when it switches off.

You want to sleep with it on. Oil-filled radiator. No fan, no exposed element, and the oil stays warm for a while after the thermostat clicks off, so the temperature stays even. It takes 20 to 30 minutes to warm up, so switch it on before bed.

You sit in one spot in a cold room. Radiant heater. It warms you and the chair directly, like sitting in the sun, so you can leave the room itself cooler. Useless for warming a room evenly, and the glowing element should not be left running unattended.

You want quiet background warmth and have a closed door. Convection panel. Slim, silent and often wall-mountable, but slow.

Step 2: Get the wattage right

Nearly every plug-in heater in the US tops out at 1,500 watts, because that is what a standard outlet supports. The rough rule is 10 watts per square foot of floor in a room with normal ceilings and decent insulation. So:

100 square feet (small office): 1,000 watts is plenty
150 square feet (bedroom): 1,500 watts
250 square feet and up (living room): a 1,500-watt heater will take the chill off but will not replace central heating

Most heaters have a low setting around 750 watts and a high setting at 1,500. The low setting is often enough once the room is warm.

Step 3: Look for the safety features

These are not extras. Do not buy a heater without them.

Tip-over switch that cuts power if the heater falls or is knocked.
Overheat protection that shuts it off if the inside gets too hot, for example when something covers the intake.
Cool-touch housing on fan heaters, so a brushed hand does not burn.
A safety listing from an independent lab, shown on the label as UL, ETL or CSA. An unlisted heater has not been tested.
A sturdy plug and thick cord. The plug should not get hot in use.

Step 4: Think about the thermostat

A heater with a thermostat switches itself off when the room reaches the temperature you set and on again when it drops. That is what keeps the electricity bill in check and keeps the room comfortable rather than swinging between cold and stuffy. Cheap heaters have a dial with no numbers; better ones show a temperature. Either works; a numbered one is easier to repeat.

An eco mode on some models runs at low power most of the time and only steps up when needed, which is worth having for long sessions.

What it costs to run

Every electric heater is the same: 1,500 watts in, 1,500 watts of heat out. So on full, every type costs the same per hour, and the cost is simply your electricity rate multiplied by 1.5 kilowatts. What changes the bill is how long it runs on full, and that comes down to the thermostat, the room’s insulation, and whether you are heating one closed room or an open house. Heating one room you are in, with the door shut, is always cheaper than turning up central heating for the whole place.

Where to put it

On the floor, on a hard, level surface. Not on a rug thick enough to block the intake, not on a table.
Three feet clear of anything that can burn: bedding, curtains, paper, furniture.
Plugged straight into the wall. No extension cords, no power strips, no adapters.
Where it will not be bumped or tripped over, and out of reach of children and pets.
For a fan heater, pointed into the room, not at a wall.

Common mistakes

Running it from a power strip.
Draping a towel over a radiator to dry it. Heaters are not for drying clothes.
Buying a radiant heater to warm a whole room.
Buying a fan heater for the bedroom and then being kept awake by it.
Leaving a heater on in an empty room; the thermostat helps, but it is not a reason to leave it unattended.

FAQ

Which type of space heater is cheapest to run?

They all turn electricity into heat at the same rate, so a 1,500-watt heater of any type costs the same per hour on full. The savings come from the thermostat cycling off, from heating only the room you are in, and from radiant heaters that warm you directly so you can set the room lower.

Is it safe to leave a space heater on overnight?

Oil-filled radiators with a thermostat, tip-over switch and overheat cut-out are the type most people run overnight, because there is no exposed element and no fan. Any heater should sit on the floor, three feet from bedding and curtains, plugged straight into the wall.

Can I plug a space heater into a power strip?

No. A 1,500-watt heater draws more than most power strips and extension cords are rated for, and they are a common cause of heater fires. Plug it directly into a wall outlet.

How many watts do I need?

About 10 watts per square foot of floor as a rough guide, so a 150-square-foot bedroom is comfortable with a 1,500-watt heater, which is the maximum a normal US outlet supports. Larger rooms need a second heater or central heating.