A standard 1,500 W space heater draws 1.5 kWh per hour — about $0.24/hour at $0.16/kWh. Run it 4 hours a day and the month is ~180 kWh ≈ $29; run it 24/7 and it’s ~1,080 kWh ≈ $173. The heater is cheap per hour and expensive per habit — the hours are the bill.

The full cost table

At the US-average-ish $0.16/kWh:

setting	hrs/day	kWh/day	$/day	$/month
750 W (low)	1	0.75	$0.12	$3.60
750 W	4	3.0	$0.48	$14.40
750 W	8	6.0	$0.96	$28.80
1,500 W	1	1.5	$0.24	$7.20
1,500 W	4	6.0	$0.96	$28.80
1,500 W	8	12.0	$1.92	$57.60
1,500 W	24	36.0	$5.76	$172.80

Your rate moves everything linearly: at $0.23/kWh the 4-hour row is ~$41/month; at $0.30 it’s ~$54. Find yours by dividing last bill’s total by its kWh — reading your bill shows where to look.

Two honest caveats

The nameplate is a ceiling. A heater on a thermostat cycles off once the room is warm, so real draw is usually below the nameplate-hours math — the table is your worst case, and mild rooms land under it.

Heater vs central heat. One room you’re sitting in: the heater wins — ~$1/day for 4 evening hours beats reheating the whole house. Whole-home warmth: central heat wins on total cost, and a heat pump wins by 2–3× over any resistive heater. The strategy is zone heating, not replacing the furnace.

Where the heater sits among everything else’s appetite — and the formula behind all of it — is in watts to kWh. The estimator on the home page runs the same math across every device at once.

A safety footnote that’s not optional: plug heaters straight into a wall outlet — never an extension cord or power strip — and keep the clearance zone clear. The math is cheap; the cord isn’t rated for it.

Frequently asked questions

Is a 1,500-watt space heater expensive to run?

Per hour, no — 1.5 kWh ≈ $0.24 at $0.16/kWh. Per month, it depends entirely on hours: 4 h/day is ~$29, overnight-every-night is ~$58, and 24/7 is ~$173. The wattage is fixed; the bill is a function of the thermostat knob.

Does an oil-filled radiator cost less than a fan heater?

Not at equal wattage — 1,500 W is 1,500 W regardless of what warms up. The real difference is duty cycle: oil-filled units hold heat and cycle off sooner, so they often draw full power less of the time. Efficiency claims like 'uses 40% less energy' on equal-wattage heaters are mostly marketing.

Why are space heaters always 1,500 watts?

It's the US outlet ceiling, not physics. A 120 V / 15 A circuit maxes at 1,800 W, and continuous-load safety guidance keeps sustained draw at ~80% — so manufacturers converge on 1,500 W (12.5 A) as the safe national standard. 'Low' settings are usually ~750 W.

Is it cheaper to run a space heater or turn up the heat?

For one occupied room, the heater usually wins: 4 hours ≈ $1/day versus reheating the whole house. For whole-home comfort, central heat wins on total cost — and a heat pump beats resistive heating 2–3× on the same warmth. Zone a room you're sitting in, never the whole house.

Do heaters use power when they're off?

A heater that's actually off draws zero — there's no standby circuit to speak of on most models. But 'thermostat reached' isn't off: units cycle between full draw and nothing, which is why real monthly cost is usually below the nameplate-hours math.

How do I compute cost at my own electric rate?

kWh = watts × hours ÷ 1,000, then × your rate. Your real rate is bill total ÷ kWh used (it folds in delivery, riders and taxes — see reading your bill), or just use the calculator above with your number.