Space Heater Running Cost Calculator

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

Heater power rating

Hours used per day

h/day

Days used per month

days

Electricity price

$per kWh

Thermostat duty cycle

Number of heaters

Cost per month

$61.20

Energy cost for the month at the schedule entered above.

Average power draw while on: 1.5Kilowatts drawn on average during on-time, after the duty cycle.
Cost per hour of use: $0.255
Energy per day: 12Kilowatt-hours used on a typical day of use.
Cost per day: $2.04
Energy per month: 360Total kilowatt-hours added to your bill for the month.
Cost over a 4-month heating season: $244.80Same usage pattern repeated for four winter months.
Heat output while on: 5,118BTU per hour. Electric resistance heaters convert essentially all input power to heat.

Assumptions

Electric resistance heating is treated as 100% efficient — all input watts become heat.
Uses a single flat price per kWh; tiered, seasonal and time-of-use rates are not modelled.
The duty cycle is applied as a flat average over on-time; real cycling varies with weather.
Fan and control power are included in the nameplate wattage.
Heat pump or oil-filled radiator models still follow the same wattage-based cost (heat pumps excepted).

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

How this is worked out

The formula

kW = watts / 1000 x (duty cycle % / 100) x number of heaters
kWh per day = kW x hours per day
Monthly cost = kWh per day x days used x price per kWh
BTU/h = kW x 3412.14

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

What you enter

Heater power rating: Nameplate wattage on the heater or its label (most plug-in heaters are 750–1500 W).from 1 to 10000 · defaults to 1500
Hours used per day: Hours the heater is switched on each day.from 0 to 24 · defaults to 8
Days used per month: Number of days in the month you actually use the heater.from 0 to 31 · defaults to 30
Electricity price: All-in rate from your bill, including delivery charges and taxes if you want a true cost.in dollars · from 0 to 2 · defaults to 0.17
Thermostat duty cycle: Share of the on-time the element actually draws full power. Use 100% for no thermostat, 50–70% for a room that reaches setpoint.a percentage · from 1 to 100 · defaults to 100
Number of heaters: Set higher if you run several identical heaters on the same schedule.from 1 to 20 · defaults to 1

What you get back

Cost per monthmain answer: Energy cost for the month at the schedule entered above.
Average power draw while on: Kilowatts drawn on average during on-time, after the duty cycle.
Cost per hour of use
Energy per day: Kilowatt-hours used on a typical day of use.
Cost per day
Energy per month: Total kilowatt-hours added to your bill for the month.
Cost over a 4-month heating season: Same usage pattern repeated for four winter months.
Heat output while on: BTU per hour. Electric resistance heaters convert essentially all input power to heat.

What this assumes

Electric resistance heating is treated as 100% efficient — all input watts become heat.
Uses a single flat price per kWh; tiered, seasonal and time-of-use rates are not modelled.
The duty cycle is applied as a flat average over on-time; real cycling varies with weather.
Fan and control power are included in the nameplate wattage.
Heat pump or oil-filled radiator models still follow the same wattage-based cost (heat pumps excepted).

About this calculator

What this calculator does

Plug-in electric heaters are among the most expensive appliances per hour of use, because they turn kilowatts straight into heat. This calculator converts a heater's nameplate wattage into kilowatt-hours and then into money, using the electricity rate you enter.

How to use it

Power rating — read it off the label or box. Most portable heaters are 1500 W on high, 750–900 W on low. Enter the setting you actually use.
Hours per day and days per month — how long it is switched on. If you run it only on cold days, lower the day count instead of the hours.
Electricity price — use the all-in cost per kWh from your bill (total bill ÷ kWh used) rather than just the energy charge, so delivery fees and taxes are included.
Duty cycle — a heater with a thermostat does not draw full power the whole time it is "on". Once the room reaches temperature the element cycles off. In a reasonably insulated room 50–70% is typical; use 100% for a heater with no thermostat or one that never satisfies the setpoint.

Where it is approximate

Electric resistance heating is essentially 100% efficient, so the wattage-to-heat conversion is exact. The uncertainty is all in behaviour: duty cycle varies with outdoor temperature, insulation, room size and setpoint, and tiered or time-of-use rates mean your marginal price per kWh may be higher than your average. Fan-only or eco modes draw far less than the rating. Results are an energy-cost estimate, not a billed amount.

Frequently asked questions

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

At 17 cents per kWh, a 1500 W heater running at full power costs 1.5 kW x $0.17 = about 25.5 cents per hour, or roughly $2.04 for an 8-hour evening. If its thermostat cycles it at 60% duty, the same hour costs about 15 cents.

▸Should I use the high or low setting wattage?

Enter the setting you actually use. Low settings typically halve the wattage and halve the cost, but the room heats more slowly, so a thermostat-controlled heater on high may end up using a similar amount of energy overall.

▸What duty cycle should I choose?

If the heater has no thermostat, or you run it in a drafty garage where it never reaches setpoint, use 100%. For a bedroom or office that warms up and holds temperature, 50–70% is a good estimate. Halving the duty cycle halves the monthly cost.

▸Is a space heater cheaper than running central heating?

Sometimes — heating one occupied room electrically can beat heating a whole house with gas or a furnace, but per unit of heat, electric resistance is usually 2–4x more expensive than natural gas and 3x more than a heat pump. Compare cost per kWh of delivered heat, not per appliance.

▸Why is my bill higher than this estimate?

Common reasons: your marginal rate is on a higher tier or peak period than your average rate, the heater runs longer than assumed, or you entered the energy charge only and left out delivery and fixed charges. Recalculate with your total bill divided by total kWh.

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.