A portable electric space heater is a relatively high-power load and is straightforward to estimate because energy use is close to the rated wattage whenever the heating element is on. Cost depends on watts, actual runtime, electricity rate, and how often the thermostat cycles.
Read the rated wattage
Many North American household space heaters are rated around 1,500 W on high, although a specific model may offer lower settings. Use the actual label or manual rating rather than assuming one universal wattage.
Calculate kilowatt-hours (kWh) from actual heating time
A 1.5 kW heater running continuously for four hours uses about 6 kilowatt-hours (kWh). Thermostat cycling lowers that total; a properly rated plug-in energy meter can show actual use if the heater manufacturer permits that setup.
Heating one zone can cost less than the whole house, but not always
Using a space heater in one occupied room can reduce central-system demand only if the rest of the home is actually set back. Running both without changing central settings usually adds energy use.
Safety limits where and how it can be used
Plug the heater directly into a suitable wall outlet, not an extension cord or power strip, and keep it away from textiles and traffic areas. If the outlet or plug becomes hot, stop using it and have the condition checked.
Sources
- U.S. Department of Energy — Energy Saver — Residential energy efficiency, heating and cooling, and equipment use.