Space Heater Cost Calculator

Estimate what a space heater costs to run per hour, day and month from its wattage, hours of use per day and your electricity rate.

Heater wattage

Hours used per day

h/day

Electricity price

$per kWh

Days used per month

days

Thermostat duty cycle

Number of heaters

Cost per month

$61.20

Effective power draw: 1.5Average kilowatts drawn while the heater is switched on.
Cost per hour of use: $0.255
Energy per day: 12Kilowatt-hours consumed each day.
Cost per day: $2.04
Energy per month: 360Kilowatt-hours added to your bill in the month.
Cost for a 4-month heating season: $244.80
Cost if used year-round: $734.40

Assumptions

Assumes an electric resistance heater, where roughly 100% of input electricity becomes heat.
Assumes a single flat electricity price per kWh, including delivery charges and taxes.
Duty cycle is applied as a simple average fraction of on-time at full rated wattage.
Fan and control electronics are assumed to be included in the nameplate wattage.
Heating-season figure assumes 4 months of identical usage; annual figure assumes 12.

Built with AI from a visitor’s request · not yet reviewed

How this is worked out

The formula

Effective kW = watts x heaters x (duty cycle / 100) / 1000
kWh per day = effective kW x hours per day
Cost per day = kWh per day x price per kWh
Cost per month = cost per day x days used per month

Open How it’s calculated above to see this worked through with your own numbers.

What you enter

Heater wattage: Check the nameplate or manual. Most portable heaters are 750 W (low) or 1500 W (high).from 50 to 10000 · defaults to 1500
Hours used per day: Hours the heater is switched on each day.from 0 to 24 · defaults to 8
Electricity price: From your utility bill: total bill divided by kWh used, including delivery charges.in dollars · from 0 to 2 · defaults to 0.17
Days used per month: Use 30 for a typical full month, or fewer if you only heat on some days.from 1 to 31 · defaults to 30
Thermostat duty cycle: Share of the switched-on time the element actually draws power. Use 100% for no thermostat, 50–70% once a room is warm.a percentage · from 5 to 100 · defaults to 100
Number of heaters: How many identical heaters run on this schedule.from 1 to 20 · defaults to 1

What you get back

Cost per monthmain answer
Effective power draw: Average kilowatts drawn while the heater is switched on.
Cost per hour of use
Energy per day: Kilowatt-hours consumed each day.
Cost per day
Energy per month: Kilowatt-hours added to your bill in the month.
Cost for a 4-month heating season
Cost if used year-round

What this assumes

Assumes an electric resistance heater, where roughly 100% of input electricity becomes heat.
Assumes a single flat electricity price per kWh, including delivery charges and taxes.
Duty cycle is applied as a simple average fraction of on-time at full rated wattage.
Fan and control electronics are assumed to be included in the nameplate wattage.
Heating-season figure assumes 4 months of identical usage; annual figure assumes 12.

About this calculator

What this calculator does

Electric resistance heaters are simple to cost out: essentially all the electricity they draw becomes heat, so the running cost depends only on how much power they pull, how long they run and what your utility charges.

Enter the heater's wattage (from the label — 1500 W is the standard maximum for a 120 V plug-in unit), the hours you run it per day, and your electricity price in dollars per kilowatt-hour. The calculator converts watts to kilowatts, multiplies by hours to get kilowatt-hours, and multiplies by your rate.

Using the duty cycle

A heater with a thermostat does not draw full power the whole time it is switched on: it cycles off once the room reaches temperature. If your heater is on 8 hours but the element only fires about 60% of that time, set the duty cycle to 60% for a much more realistic monthly figure. Leave it at 100% for a worst-case estimate or for a heater run continuously on high with no thermostat.

Where it is approximate

Use your all-in electricity price, not just the energy charge — delivery, riders and taxes often add several cents per kWh. If you are on a time-of-use or tiered plan, the marginal rate for the hours you heat may be higher than your average rate, so run the numbers with that rate instead. Fan-only power draw, voltage variation and real-world thermostat behaviour cause small differences from the calculated value. Heat pumps and gas heaters do not follow this model, since they deliver more heat than the electricity or fuel energy they consume at the plug.

Frequently asked questions

▸How much does a 1500 W space heater cost per hour?

A 1500 W heater draws 1.5 kWh per hour at full power. At $0.17 per kWh that is about $0.26 per hour, or roughly $0.15 per hour at $0.10 per kWh. Multiply 1.5 by your own rate to get the exact figure, then reduce it if the thermostat cycles the element off part of the time.

▸Where do I find my price per kWh?

Divide your total monthly electricity bill by the kilowatt-hours shown on it. That captures energy plus delivery, fees and taxes, which is the number that actually matters. If you are on a time-of-use plan, use the rate that applies during the hours you run the heater.

▸Is running a space heater cheaper than central heating?

It can be, if you heat one occupied room and turn the central system down. But per unit of heat, electric resistance heating is usually the most expensive option, costing two to four times more than a heat pump and often more than natural gas. Heating a whole house with plug-in heaters is rarely cheaper.

▸Does a heater on the 'low' setting cost less?

Yes, proportionally. A heater switched from 1500 W to 750 W costs half as much per hour, though it may need to run longer to reach the same room temperature. Enter the setting's wattage rather than the maximum rating.

▸What duty cycle should I use?

For a heater with no thermostat, or one running flat out in a cold, poorly insulated space, use 100%. In a small, reasonably insulated room that has already warmed up, 40–70% is typical. If you want a firm answer, plug the heater into an energy meter for a day and compare measured kWh with the calculator.

How this calculator was made

A visitor asked for: “Cost to run a space heater for a month from its wattage, hours used per day and the price per kilowatt-hour”. An AI model wrote the formulas as a declarative spec, our engine checked that every expression parses and evaluates, and the math above runs deterministically in your browser. It hasn’t been reviewed by a person yet — check the assumptions and the How it’s calculated panel before relying on it.