The easiest way to work out how much an electric boiler will cost to heat your property is to check your annual heat use via your existing energy bill. This will be shown in kilowatt hours for a gas boiler. Multiply the number of kWh by your electricity tariff, to find your annual electric heating running costs. You may find the amount of kWh used by your electric boiler is lower than that of your gas or oil boiler because it is more efficient, so that figure will be reduced.