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.
Space Heater Running Cost Calculator: with the default inputs, cost per month is $61.20.
Nameplate wattage. Most portable plug-in heaters are 750 W, 1000 W or 1500 W.
How many hours per day the heater is switched on.
Share of the on-time the element actually draws full power. Use 100% for no thermostat, 50-70% once a room is up to temperature.
Your all-in rate including delivery charges, from your utility bill.
Use 30 for a typical month, or fewer if you only heat on some days.
Set above 1 to total up several identical heaters.
Energy cost for the days and hours entered.
- Average draw while on
- 1.5Kilowatts drawn on average during running hours.
- Cost per hour of use
- $0.255
- Energy per day
- 12Kilowatt-hours used on a day of typical use.
- Cost per day
- $2.04
- Energy per month
- 360Kilowatt-hours added to your monthly bill.
- Cost over a 5-month heating season
- $306.00
- Cost if used all year
- $744.60
- Current draw at 120 V (full power)
- 12.5Compare with your circuit rating: a 15 A circuit should stay under about 12 A continuous.
Assumptions
- Assumes an electric resistance heater that converts essentially 100% of its electricity into heat (efficiency ≈ 1).
- Uses a flat price per kilowatt-hour; tiered, seasonal and time-of-use rates are not modelled.
- Cost per year assumes the same daily usage on all 365 days, which overstates seasonal heating.
- Current draw is computed at 120 V; halve it for a 240 V circuit.
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 Cost per day = kWh per day x price per kWh Cost per month = cost per day x days used per month Amps at 120 V = total watts / 120
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 many hours per day the heater is switched on.from 0 to 24 · defaults to 8
- Thermostat duty cycle
- Share of the on-time the element actually draws full power. Use 100% for no thermostat, 50-70% once a room is up to temperature.a percentage · from 1 to 100 · defaults to 100
- Electricity price
- Your all-in rate including delivery charges, from your utility bill.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 to total up several identical heaters.from 1 to 20 · defaults to 1
What you get back
- Cost per monthmain answer
- Energy cost for the days and hours entered.
- Average draw while on
- Kilowatts drawn on average during running hours.
- Cost per hour of use
- Energy per day
- Kilowatt-hours used on a day of typical use.
- Cost per day
- Energy per month
- Kilowatt-hours added to your monthly bill.
- Cost over a 5-month heating season
- Cost if used all year
- Current draw at 120 V (full power)
- Compare with your circuit rating: a 15 A circuit should stay under about 12 A continuous.
What this assumes
- Assumes an electric resistance heater that converts essentially 100% of its electricity into heat (efficiency ≈ 1).
- Uses a flat price per kilowatt-hour; tiered, seasonal and time-of-use rates are not modelled.
- Cost per year assumes the same daily usage on all 365 days, which overstates seasonal heating.
- Current draw is computed at 120 V; halve it for a 240 V circuit.
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 is just power multiplied by time multiplied by your electricity rate.
Enter the heater's nameplate wattage (printed on the label or in the manual — 1500 W is the maximum for a standard North American plug-in unit), how many hours a day you run it, and the price you pay per kilowatt-hour. The calculator returns cost per hour, per day, per month, and per year, plus the kilowatt-hours added to your bill.
Getting the numbers right
Use your all-in electricity rate. Divide your total bill by the kilowatt-hours used to capture delivery, riders and taxes — this is often 30-60% higher than the headline energy rate.
Use the duty cycle. A thermostatically controlled heater runs at full power only until the room reaches its setpoint, then cycles. Left at 100%, this calculator gives the worst case (continuous full power). If the heater is holding an already-warm room, 50-70% is more realistic. A heater on a "low" setting draws its low wattage, so enter that wattage instead.
Where it's approximate
Actual duty cycle depends on insulation, outdoor temperature, room size and setpoint, so treat the monthly figure as a range rather than a precise bill. The current-draw output assumes 120 V and full rated power; on a 240 V circuit the amps will be about half. Costs also ignore tiered or time-of-use pricing, which can push a high-use month into a more expensive rate block.
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. At $0.17/kWh that is about 25.5 cents per hour, or roughly $2.04 for an 8-hour day and $61 over a 30-day month. Change the electricity price field to match your own bill.
▸Do 'energy-saving' space heaters cost less to run?
Not at the same wattage. Ceramic, oil-filled, infrared and fan heaters all turn one kilowatt-hour of electricity into the same amount of heat. Savings come only from running fewer watts for fewer hours — for example, using a thermostat, a timer, or heating one occupied room instead of the whole house.
▸What duty cycle should I enter?
Use 100% if the heater has no thermostat, is on its highest setting in a cold room, or you want a worst-case number. Use 50-70% for a thermostat holding a reasonably insulated room at temperature. Measuring with a plug-in energy monitor for a day is the most accurate approach.
▸Is a space heater cheaper than my central heating?
Sometimes. Electric heaters are cheap only if they let you turn the main system down and heat a small area. Per unit of heat, natural gas and heat pumps are usually far less expensive, because a heat pump delivers 2-4 units of heat per unit of electricity while a resistance heater delivers 1.
▸Can I run two 1500 W heaters on one circuit?
No. Two 1500 W heaters draw 25 A at 120 V, well beyond a 15 A or 20 A branch circuit. A single 1500 W heater at 12.5 A already exceeds the 80% continuous-load guideline for a 15 A circuit, so it should be the only significant load on it.
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.