Electric resistance heaters make cost estimation straightforward: convert watts to kilowatts, multiply by active runtime, and apply the electricity rate. The difficult input is how long the heater actually draws full power.
Read the heater's wattage
Use the rating label or product documentation. Many portable electric heaters have more than one setting, so enter the wattage for the mode you expect to use.
A 1,500-watt heater equals 1.5 kilowatts. If it draws full power for one hour, it consumes 1.5 kilowatt-hours.
- Kilowatts = watts ÷ 1,000
- kWh = kilowatts × active hours
- Cost = kWh × electricity rate
Separate elapsed time from active runtime
A thermostat-controlled heater may cycle off after the room warms. Six hours in the room does not always mean six hours at full wattage.
For a planning range, calculate a full-runtime case and a lower-duty-cycle case. A plug-in energy meter can provide a better measurement for the exact heater and room.
Use your marginal electricity rate
The energy portion of the utility bill is usually expressed in dollars per kWh. Time-of-use pricing may require separate calculations for different hours.
Fixed customer charges normally do not rise because the heater ran for another hour. Taxes, tiers, and demand charges can make an exact bill estimate more complicated.
Cost does not answer the heating question
The Department of Energy explains that a small heater can make sense for heating one occupied room instead of overheating an entire home. That does not mean every portable heater will cost less than every central system.
Room size, insulation, outdoor temperature, central-system efficiency, fuel price, and how much of the home is heated all affect the comparison. Follow current manufacturer and fire-safety instructions.
Multiply rated kilowatts by active heater hours and your electricity rate; use a range when thermostat cycling is unknown.
Frequently asked questions
How much does a 1,500-watt heater use per hour?
At continuous full power it uses 1.5 kWh per hour. Multiply 1.5 by the electricity rate for hourly energy cost.
Will a thermostat reduce space-heater cost?
It can reduce active runtime after the room reaches temperature. The savings depend on room heat loss, setting, heater controls, and how often the element cycles.
Sources and further reading
Sources support the methods and practical guidance above. Product specifications and local requirements should take priority for a specific project.
U.S. Department of Energy: Small Space Heaters Official guidance on appropriate use, heater types, selection, and safety. ↗