The oil heaters I am familiar with have a high and low setting switch with the high setting using 2000W and the low setting 1200W. So, while it is running the high setting uses more.

However, if you are controlling the heater with a thermostat control then it makes no (or almost no difference). On both settings the heater will just heat up to the dialed in temperature then stop. On the high setting it gets there faster than on the low setting, but both will use approximately the same amount of energy to get there and the same amount of power to hold that setting.

Energy (kWh) is equal to the power (kW) times the time it runs in hours.

If it takes 1kWh to get the oil heater up to temperature then the 2kW setting will get there in approx half an hour (2kW x 0.5 hours = 1 kWh). The 1.2kW setting will rake approx 50 minutes (1.2kW x 50/60 hours = 1kWh).

I'm simplifying this (ignoring heat lost into the room), but basically they will work out the same if they're running on the thermostat.

Written in July 2008