Space Heater Cost Calculator

How it is calculated

Power is in watts, hours is the running time per day (above 0 and at most 24), days is the number of days and the rate is the price per kWh, in dollars. The engine converts to energy first: kWh = watts × hours × days ÷ 1000. The costs follow: total = kWh × rate and cost per day = watts × hours ÷ 1000 × rate. All four fields must be above zero, and days may be a fraction. The tool assumes the heater draws its full rated wattage for every hour you enter. A heater with a thermostat that cycles off will use less, so for such a heater enter the hours it is actually drawing power, not the hours it is switched on.

Common mistakes

• Typing the rate in cents (15) instead of in currency units per kWh (0.15), which multiplies the total by 100.
• Entering the heater's rated watts when the thermostat holds the heater off for part of each hour; the tool then overstates the bill because it assumes full power the whole time.
• Putting the hours for the whole period in the hours field. Hours means hours per day and cannot exceed 24; put the period in the days field.
• Using the energy figure in kW rather than watts. A 1.5 kW heater must be entered as 1500.
• Leaving out fixed charges, taxes and tiered tariffs: the tool multiplies by one flat rate per kWh, so a bill with a higher night or peak rate will not match.