Space Heater Running Cost Calculator

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

Heater power rating

Hours used per day

hours

Thermostat on-time (duty cycle)

Electricity price

$per kWh

Days used per month

Number of heaters

Length of heating season

months

Cost per month

$61.20

Cost per hour of use: $0.255Average cost for each hour the heater is switched on.
Energy used per day: 12Kilowatt-hours per day.
Cost per day: $2.04
Energy used per month: 360Kilowatt-hours added to your monthly bill.
Cost for the heating season: $306.00
Heat output at full power: 5,118BTU per hour delivered while the element is drawing full power.

Assumptions

Assumes an electric resistance heater that converts essentially 100% of the electricity it draws into heat.
Uses a single flat electricity price per kWh; tiered, seasonal and time-of-use rates are not modelled.
Duty cycle is entered by the user and assumed constant over the month.
Full-power wattage is taken from the nameplate; real draw can vary with supply voltage.
BTU output uses 3.412 BTU per watt-hour.

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

How this is worked out

The formula

kW = watts / 1000
Effective load = kW x (duty cycle / 100) x number of heaters
kWh per day = effective load 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
BTU/hr = watts 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 plug-in heaters are 750 W (low) or 1500 W (high).from 1 to 10000 · defaults to 1500
Hours used per day: How many hours per day the heater is switched on.from 0 to 24 · defaults to 8
Thermostat on-time (duty cycle): Share of switched-on time the element actually draws power. Use 100% for constant output, 50–70% if the thermostat cycles.a percentage · from 1 to 100 · defaults to 100
Electricity price: All-in rate from your bill, including delivery charges and taxes.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
Number of heaters: A number.from 1 to 20 · defaults to 1
Length of heating season: Used only for the seasonal total.from 1 to 12 · defaults to 5

What you get back

Cost per monthmain answer
Cost per hour of use: Average cost for each hour the heater is switched on.
Energy used per day: Kilowatt-hours per day.
Cost per day
Energy used per month: Kilowatt-hours added to your monthly bill.
Cost for the heating season
Heat output at full power: BTU per hour delivered while the element is drawing full power.

What this assumes

Assumes an electric resistance heater that converts essentially 100% of the electricity it draws into heat.
Uses a single flat electricity price per kWh; tiered, seasonal and time-of-use rates are not modelled.
Duty cycle is entered by the user and assumed constant over the month.
Full-power wattage is taken from the nameplate; real draw can vary with supply voltage.
BTU output uses 3.412 BTU per watt-hour.

About this calculator

What this calculator does

Electric resistance heaters are simple to price: essentially all the electricity they draw becomes heat, so the cost is just energy used multiplied by your electricity rate. This calculator converts a heater's wattage and your usage pattern into kilowatt-hours and dollars per hour, per day, per month and for a whole heating season.

How to use it

Enter the nameplate wattage printed on the heater or its label — 1500 W is the standard maximum for a 120 V plug-in unit, and many models also have a 750 W setting. Add how many hours a day you run it, how many days a month, and your all-in electricity price per kilowatt-hour. Take that price from a recent bill by dividing the total amount owed by the kilowatt-hours billed; that captures delivery charges and taxes, not just the energy rate.

The thermostat on-time field matters a lot. A heater with a thermostat does not draw full power continuously — once the room reaches the set temperature the element cycles off. If you set 1500 W but the heater only fires half the time, your real cost is half of the full-power figure. Leave it at 100% for a worst-case estimate, or drop it to 50–70% for typical thermostat-controlled use.

Where it is approximate

Actual duty cycle depends on room size, insulation, outdoor temperature and thermostat setting, so treat the result as a range rather than an exact bill amount. Tiered or time-of-use rates, demand charges and fan-only power draw are not modelled. The calculator also does not compare heating fuels — a heat pump delivers several times more heat per kilowatt-hour than a resistance heater.

Frequently asked questions

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

At full power it uses 1.5 kWh per hour, so the cost is 1.5 x your electricity price. At $0.17/kWh that is about $0.26 per hour, or roughly $2.04 for an 8-hour day and about $61 a month at 30 days. If the thermostat cycles the element off half the time, halve those figures.

▸What should I use for the thermostat on-time?

Use 100% if the heater runs flat out (very cold room, high setting, or no thermostat). For a well-insulated room held at a comfortable temperature, 40–70% is typical. If you have a smart plug with energy monitoring, compare its measured kWh with the full-power figure to find your real duty cycle.

▸Where do I find my true price per kWh?

Divide the total amount of a recent electricity bill by the kilowatt-hours it billed. That all-in figure includes supply, delivery, fixed-ish charges and taxes, and is usually noticeably higher than the advertised energy-only rate.

▸Do low, medium and high settings change the cost?

Yes. Settings change the wattage drawn, so a 750 W setting costs half as much per hour as 1500 W. Enter the wattage of the setting you actually use. A lower setting may need to run longer, so the total energy difference is often smaller than it looks.

▸Is a space heater cheaper than central heating?

Sometimes. Heating one small room electrically can beat heating the whole house with a furnace, but per unit of heat, electric resistance is one of the most expensive options. A heat pump typically delivers 2–4 times more heat per kWh, and natural gas is often cheaper per BTU.

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.