How many watts does a space heater use?

A space heater uses 900–1,500 watts while running, which is 7.5–12.5 amps at 120 V.

Space heater watts, amps and circuit

Typical power use of a space heater
Running watts	900–1,500 W
Voltage	120 V
Running amps	7.5–12.5 A
Circuit	standard 120 V outlet

Also called: electric heater, portable heater, small space heater, 1500 watt heater, oil-filled radiator heater.

Space heater watts by size and type

Running and starting watts of space heater types
Size or type	Running watts, W	Volts, V	Amps, A	Starting watts, W
Space heater	900–1,500	120	7.5–12.5	—
Standard heater, low setting	900	120	7.5	—
Standard heater, high setting	1,500	120	12.5	—
Oil-filled radiator, high setting	1,500	120	12.5	—

Watts of space heater types. The lighter part of a bar is the upper end of the typical range.

What size generator runs a space heater?

A space heater needs a generator that supplies at least 1,500 running watts. A 2,000 W generator covers it with its running rating alone; add the watts of anything else you run at the same time.

How long a portable power station runs a space heater

Runtime of a space heater on a portable power station, at 85% inverter efficiency
Battery capacity, Wh	At 1,500 W, h	At 900 W, h
500	0.3	0.5
1,000	0.6	0.9
2,000	1.1	1.9
3,600	2	3.4

A 500 Wh portable power station runs a space heater drawing 1,500 W for about 0.3 hours at 85% inverter efficiency. Runtime = capacity × 85% ÷ watts; the 85% efficiency is an assumption. The power station's AC output must be at least 1,500 W.

What it costs to run a space heater

Running a space heater at 1,200 W, the middle of its 900–1,500 W range, for one hour a day uses 438 kWh a year. That costs about $79 a year at $0.18 per kWh, the US average residential price for August 2026.

Power

Use per day

Electricity price

$/kWh

Your bill's total ÷ kWh used. 0.18 is the US residential average.

Result

$6.57 / month

Per day: $0.22
Per year: $79
Energy per day: 1.2 kWh
Energy per month: 36.5 kWh

How it is calculated

kWh per day = 1,200 W × 1 h ÷ 1,000 = 1.2
Per month = 1.2 kWh × 30.4 days × $0.18 = $6.57

What affects space heater power use

The heaters checked, a Lasko ceramic heater and a De'Longhi oil-filled radiator, are rated 1,500 W on their high setting; the Lasko runs at 900 W on low. A thermostat cycles the element, so the draw over an hour is often lower than the rating. All electric resistance heaters turn the same watts into the same heat, whatever their style.

How the amps are calculated

Amps = watts ÷ volts. For 1,500 W at 120 V that is 12.5 A. The 900–1,500 W range covers typical models; the nameplate on a space heater gives the exact figure.