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What The Oil-Filled Radiator Cost Calculator Works Out
- Per day: rating in kW x hours on x the thermostat duty cycle gives the kilowatt-hours used, multiplied by the electricity unit rate. A 2kW radiator holding a warm room at 60% duty for five evening hours uses 6 kWh, about GBP 1.58 at the current Ofgem price cap rate (26.32p per kWh from October 2026) rather than the GBP 2.63 of the flat-out number.
- Per month: the daily cost x 30. Every resistive heater converts electricity to heat at the same 100%, so the oil's genuine contribution is the duty cycle: thermal mass smooths output and a warm room holds on 40% to 60% of rated draw.
- Worth knowing: the flat-out hourly cost of a 2kW unit, about 53p at the current price cap rate. Physics, not brand; the thermostat and a well-insulated room bring the real number down.
- Electricity unit rate (advanced): defaults to the current Ofgem price cap unit rate but is editable for your own tariff or an off-peak rate.
- Custom duty cycle (advanced): set your own percentage when the presets do not fit. A modern electronic thermostat with a timer does more for the bill than any wattage choice.
- Number of radiators and heating months (advanced): scale up for several rooms and turn the monthly figure into a season. Five months (November to March) is typical for a home office or cold corner.
- Per hour flat out (advanced): the rated kW x unit rate, with the duty-adjusted hourly figure alongside.
- Same heat from gas central heating (advanced): the season's kilowatt-hours bought as gas at your unit rate through a 90% efficient boiler, roughly a third of the electric cost. The radiator's niche is the genuinely single-heated room while the boiler sleeps; the classic false economy is the radiator running beside a boiler that never turned down.
- Right size for the room (advanced): about 100W per square metre of floor is the rough sizing rule for an average room. An undersized unit runs at 100% duty and loses its whole advantage. Sealed oil never needs topping up, tip-over cut-outs are standard on anything reputable, and drying clothes on the fins is the one prohibited folk use.