Space Heater Running Cost Calculator

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

Heater power rating

Hours used per day

Thermostat duty cycle

Electricity price

$per kWh

Days used per month

Number of heaters

Cost per month

$61.20

Electricity cost for the whole month of use.

Energy used per month: 360Kilowatt-hours added to your bill each month.
Cost per day: $2.04
Energy used per day: 12
Cost per hour of use: $0.255Average cost for each hour the heater is switched on, allowing for thermostat cycling.
Full-power hours per month: 240Equivalent hours at full rated wattage.
Cost per year at this rate: $734.40If you ran the heater this way all 12 months.
Heat output while on: 5,118BTU per hour at full power (electric resistance heaters are ~100% efficient).

Assumptions

Assumes an electric resistance heater, which converts essentially all input electricity to heat.
Uses a single flat electricity price; tiered, time-of-use and demand charges are not modelled.
Assumes the heater draws its full rated wattage whenever the element is on; the duty cycle accounts for thermostat cycling.
A 'month' is whatever number of use-days you enter (default 30); the yearly figure simply multiplies the month by 12.

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

How this is worked out

The formula

kWh per month = (watts / 1000) x hours per day x (duty cycle / 100) x heaters x days per month
Cost per month = kWh per month x price per kWh
Cost per hour = (watts / 1000) x (duty cycle / 100) x heaters x price per kWh
BTU/h = watts x heaters x 3.412

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

What you enter

Heater power rating: Nameplate wattage. Most portable plug-in heaters are 750 W, 1000 W or 1500 W.from 1 to 10000 · defaults to 1500
Hours used per day: How long the heater is switched on each day.from 0 to 24 · defaults to 8
Thermostat duty cycle: Share of the switched-on time the element actually draws power. Use 100% for no thermostat, 50-70% for typical cycling.a percentage · from 1 to 100 · defaults to 100
Electricity price: All-in rate from your bill, including delivery charges if you want the true cost.in dollars · from 0 to 5 · defaults to 0.17
Days used per month: Use 30 for a typical month, or fewer if you only heat on some days.from 1 to 31 · defaults to 30
Number of heaters: Set above 1 if several identical heaters run on the same schedule.from 1 to 20 · defaults to 1

What you get back

Cost per monthmain answer: Electricity cost for the whole month of use.
Energy used per month: Kilowatt-hours added to your bill each month.
Cost per day
Energy used per day
Cost per hour of use: Average cost for each hour the heater is switched on, allowing for thermostat cycling.
Full-power hours per month: Equivalent hours at full rated wattage.
Cost per year at this rate: If you ran the heater this way all 12 months.
Heat output while on: BTU per hour at full power (electric resistance heaters are ~100% efficient).

What this assumes

Assumes an electric resistance heater, which converts essentially all input electricity to heat.
Uses a single flat electricity price; tiered, time-of-use and demand charges are not modelled.
Assumes the heater draws its full rated wattage whenever the element is on; the duty cycle accounts for thermostat cycling.
A 'month' is whatever number of use-days you enter (default 30); the yearly figure simply multiplies the month by 12.

About this calculator

What this calculator does

Electric space heaters are among the biggest single loads in a home, and the arithmetic that tells you what one costs is simple: power multiplied by time multiplied by price. This calculator converts a heater's nameplate wattage into kilowatt-hours and then into money, for an hour, a day, a month and a full year.

How to use it

Enter the heater's wattage — it is printed on the label or in the manual, and portable units are usually 750 W, 1000 W or 1500 W. Add the number of hours per day you switch it on and the number of days per month you use it. Then enter your electricity price per kilowatt-hour; for a realistic answer use the all-in rate from your bill (energy plus delivery and taxes divided by kWh used), not just the supply rate.

The duty cycle field matters a lot. A heater with a thermostat does not draw power the whole time it is on — once the room reaches temperature the element cycles off. If your heater keeps a small room comfortable and clicks off often, 50–70% is a fair estimate. Leave it at 100% for a heater running flat out or with no thermostat.

Where it is approximate

Electric resistance heating is essentially 100% efficient, so wattage converts directly to heat and there is no efficiency term to guess at. The uncertainty is all in the duty cycle and in your real electricity rate, especially on time-of-use or tiered tariffs where the marginal price of extra heating can be higher than your average price. Fan-only or eco settings draw less than the rated wattage, so treat the result as an upper bound for those modes.

Frequently asked questions

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

At full power a 1500 W heater uses 1.5 kWh per hour. Multiply by your rate: at $0.17/kWh that is about $0.26 per hour, or roughly $2.04 for an 8-hour day. If the thermostat cycles the element off half the time, the effective cost falls to about $0.13 per hour.

▸Should I use my supply rate or my total rate per kWh?

Use the total. Divide the full amount of a recent bill by the kilowatt-hours it covered to get an all-in rate that includes delivery, riders and taxes. That is the money you actually avoid by running the heater less.

▸What duty cycle should I enter?

If the heater runs continuously without reaching its set point, use 100%. In a well-insulated small room where the unit clicks on and off, 50–70% is typical. If you are unsure, run the numbers at both 100% and 60% to see the range.

▸Is a space heater cheaper than central heating?

Sometimes. Heating one room electrically can beat heating the whole house, but per unit of heat electric resistance is usually more expensive than natural gas, and a heat pump delivers 2–4 times more heat per kWh. Compare the cost per month here against your heating fuel cost for the same period.

▸Does a higher wattage heater cost more to run?

Per hour of operation, yes — it draws proportionally more power. But a larger heater reaches the target temperature sooner and then cycles off, so total daily energy depends mainly on how much heat the room loses, not on the size of the heater.

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.