A common explanation says carbon heaters use less electricity because they emit far infrared, while ceramic fan heaters use a lot. On the efficiency of turning electricity into heat, that distinction does not hold. Run any type at the same wattage for the same time and it uses the same energy.
Resistive heaters all turn electricity into heat
The space heater buying guide from Save on Energy, the conservation program of Ontario's Independent Electricity System Operator (IESO), explains why space heaters, unlike many other appliances, are not certified under ENERGY STAR: any electric heater is 100% efficient at converting electricity to heat. So from an energy-efficiency standpoint you can compare models simply by the watts on the package, and two models with the same watts use the same energy under the same circumstances for the same time.
Carbon, halogen, ceramic and oil-filled heaters differ in heating element material or in how they release heat, but all are electric heaters. Energy use is set by watts multiplied by time.
What differs is how heat is delivered
The same guide explains the types by heat delivery. Fan-forced convection heaters warm the surrounding air and suit warming a room quickly; radiant heaters, including infrared, give direct heat to an object such as a person rather than to the air, and are a good option if you stay in one place and want direct heat. Oil-filled heaters warm up and cool down slowly and give residual warmth after being turned off.
So the claim that a carbon heater uses less is true in a specific case. If one person at a desk only needs to be warm and a 900 W radiant unit is enough, it uses less electricity than running a 2,000 W fan heater to warm all the air in the room. What is saved there is wattage and running time. The guide likewise advises using the lowest wattage that meets your needs. If all the air in the room must reach the same temperature, every type has to make that much heat from electricity.
Calculating with watts and hours
The table shows a monthly upper bound assuming the heater runs nonstop at full output, 4 hours a day for 30 days. A heater whose thermostat cycles the element uses less.
| Assumption | Power (W) | Daily use (h) | Monthly energy (kWh, 30 days) |
|---|---|---|---|
| Tabletop radiant | 900 | 4 | 108 |
| Fan heater / oil-filled (high) | 2,000 | 4 | 240 |
The formula is W ÷ 1,000 × hours × 30. For 900 W, 0.9 × 4 × 30 = 108 kWh; for 2,000 W, 2 × 4 × 30 = 240 kWh. The wattage at each high/low setting varies by product, so recalculate using the rated power on the label or in the manual. When converting kWh into a bill, which progressive tier your household's existing usage falls in decides the result; the method is covered in how to calculate the electricity cost of electric blankets and hot-water mats.
What really differs in efficiency is a heat pump
In electric heating, going beyond 100% happens with a heat pump, which moves heat rather than making it, such as the heating mode of a heat-pump air conditioner. takeCHARGE, an energy conservation program in Newfoundland and Labrador, Canada, states in its comparison of heat pumps and baseboard heaters that resistive heating is 100% efficient while heat pumps can be as much as 200% to 300% efficient, adding that efficiency varies with the type of heat pump, the unit's specifications and the outside temperature.
Producing the same heat as the 2,000 W heater above with a heat pump at 200% to 300% efficiency takes 1,000 W to about 667 W. At the same 4 hours a day for 30 days, that is 120 kWh to 80 kWh. Actual efficiency can fall outside this range depending on the model and the outdoor temperature, and the comparison assumes a room that already has a heat-pump air conditioner.