Heating and heat pump tools

Do space heaters use a lot of electricity?

Yes — but how much depends almost entirely on two numbers nobody publishes with their answer: how many hours the heater is switched on, and how much of that time the thermostat actually keeps the element energised.

How much electricity does a space heater use?

A 1,500 W portable heater running eight hours a day with the element always on uses 12.0 kWh a day and 365.2 kWh per average month — $65.74 per month at $0.180/kWh, or $0.270 for every hour the element runs. That is roughly 10× the monthly consumption of a typical refrigerator (38.4 kWh). Let the thermostat cut the element out half the time and the same eight hours of comfort costs $32.87 instead of $65.74. So the honest answer is that a space heater is a large load per hour and a modest or a very large load per month, depending on duty cycle and hours — both of which you can set below.

The same heater across a realistic range of electricity rates

Almost every page answering this question fixes one rate — usually somewhere around $0.140/kWh — and reports a single dollar figure. US residential rates span more than a factor of three between states, and time-of-use tariffs move the evening hours a heater is most likely to run into the most expensive band. Each row below is a separate run of the same engine, not the first row multiplied out.

1,500 W, 8 hours a day, element on for the whole time, over an average month of 30.436875 days.
Electricity rate	Per running hour	Per day	Per average month	Per year
$0.100/kWh	$0.150	$1.20	$36.52	$438.29
$0.140/kWh	$0.210	$1.68	$51.13	$613.61
$0.180/kWh	$0.270	$2.16	$65.74	$788.92
$0.250/kWh	$0.375	$3.00	$91.31	$1,096
$0.350/kWh	$0.525	$4.20	$127.83	$1,534
$0.450/kWh	$0.675	$5.40	$164.36	$1,972

Heater setting matters as much as the rate

Same eight hours a day at $0.180/kWh, element on throughout. Portable heaters commonly offer a half-power mode; oil-filled and fan models are rated the same way.
Heater setting	Per day	Per average month	Cost per average month
400 W	3.20 kWh	97.4 kWh	$17.53
750 W	6.00 kWh	182.6 kWh	$32.87
1000 W	8.00 kWh	243.5 kWh	$43.83
1500 W	12.0 kWh	365.2 kWh	$65.74

Work out your own heater

Your heater

Heater power

Scenario: heater setting

Hours switched on

Thermostat duty cycle

Share of the switched-on hours the element is actually drawing power. A well-insulated small room can sit near 30–50%; a draughty room approaches 100%.

Scenario: room

Electricity rate

Number of heaters

$65.74

per average month

365.2 kWh per average month — 1500 W for 8 h/day at 100% duty cycle.

Calculated from your inputs

Per running hour: $0.270
Per day: $2.16
Per average month: $65.74
Per year: $788.92

Energy per average month

365.2 kWh

Rated power × duty cycle × hours, over an average month of 30.436875 days.

Average power across 24 hours

500 W

What the heater adds to your home's round-the-clock average draw.

Share of a 899 kWh month

41%

10,791 kWh a year divided by twelve — U.S. Energy Information Administration, 2022. A scale reference, not your own bill.

Same heater, recomputed at each rate: 1500 W, 8 h/day, 100% duty cycle. Every row is a separate engine run, not the first row scaled.
Electricity rate	Per running hour	Per day	Per average month	Per year
$0.100/kWh	$0.150	$1.20	$36.52	$438.29
$0.140/kWh	$0.210	$1.68	$51.13	$613.61
$0.180/kWh	$0.270	$2.16	$65.74	$788.92
$0.250/kWh	$0.375	$3.00	$91.31	$1,096
$0.350/kWh	$0.525	$4.20	$127.83	$1,534
$0.450/kWh	$0.675	$5.40	$164.36	$1,972

The same heat from a heat pump

A resistance heater turns 1 kWh of electricity into 1 kWh of heat, so the 365.2 kWh above is also the heat delivered into the room. Supplying that same heat with a heat pump at a seasonal performance factor of 3 would take 121.7 kWh of electricity, or $21.91 instead of $65.74 per average month. That is a scenario estimate: seasonal performance depends on climate, emitter temperature, sizing and controls, and a portable heater is not a like-for-like replacement for a fixed heating system.

Method

1,500 W = 1.5 kW
1.5 kW × 8 h/day = 12 kWh/day active
12 kWh × 0.18 USD/kWh = 2.16 USD/day
2.16 × 30.436875 days = 65.744 USD/month
12 kWh × 365.2425 days = 4382.91 kWh/year
4382.91 kWh × 0.18 USD/kWh = 788.924 USD/year

No efficiency factor, oversizing allowance or safety margin is applied anywhere in this calculation.

Assumptions

Electricity rate of 0.18 USD/kWh (editable).
Calculations use a year of 365.2425 days and an average month of 365.2425 ÷ 12 = 30.436875 days, so twelve average months equal one year exactly. Displayed values are rounded to 365.24 and 30.44 days, and the rounded figures do not multiply out exactly.
Rated power is treated as real power in watts, not volt-amps.
A resistance heater has no rated efficiency to apply: essentially all the electricity it draws leaves as heat in the room.
One heater modelled.

What can change the result?

Duty cycle — the single largest unknown, set by room size, insulation and outdoor temperature
Heater setting: many units run a 750 W half-power mode as well as 1,500 W
Hours of use, which typically rise sharply during a cold snap
Your actual marginal rate, including any time-of-use band the heating hours fall into
Whether the heater displaces other heating or adds to it

Why “energy-saving” heaters are not cheaper to run

Treat the number below as the cost of the heater running at full power for the hours you set. If your heater has a thermostat and the room reaches temperature, lower the duty cycle to match — 50% duty roughly halves the cost. Note that every watt of a resistance heater becomes one watt of heat, so no 'energy-saving' portable heater of the same wattage is cheaper to run.

Two heaters of the same rated power, run for the same time at the same duty cycle, consume the same electricity — whether they are ceramic, oil-filled, infrared or micathermic. What differs is how the heat is distributed and how quickly the room feels warm, which can change how long you leave the heater on. That is a real effect, but it acts through hours and duty cycle, the two inputs above, not through an efficiency figure.

The one way to deliver the same heat for materially less electricity is not a better resistance heater; it is a machine that moves heat instead of making it. Supplying the 365.2 kWh of heat in the headline case with a heat pump at a seasonal performance factor of 3 would take 121.7 kWh of electricity instead — $21.91 rather than $65.74 per average month. That is a scenario estimate under stated assumptions, and a portable unit is not a like-for-like substitute for a fixed system.

What this page does not tell you

It does not tell you whether running a space heater is cheaper than turning up your central heating. That comparison depends on how much of the home each option heats, the fuel and efficiency of the central system, and how well the heated room is separated from the rest of the house — none of which is modelled here. It also excludes any standing charge or fixed monthly fee on your bill, which does not change when the heater runs.