Oil-Filled Radiator Running Costs UK: What 0.5kW to 2.5kW Models Really Cost Per Hour

Quick answer: Oil-filled radiators cost 13p to 65p per hour flat out, depending on size (0.5kW to 2.5kW at 26.11p/kWh). In practice the thermostat cycles the element on and off, so a typical 1.5kW model costs closer to 24p an hour once the room is up to temperature.

All costs on this page are calculated at the July–September 2026 Ofgem price cap for Direct Debit customers: 26.11p per kWh of electricity, with gas comparisons at 7.33p per kWh. Unit rates vary slightly across the 14 GB regions, so treat these as good averages and check the rate on your own bill.

The sum behind every figure on this page

Power in kilowatts × hours = kilowatt-hours (kWh), and each kWh costs 26.11p at the current cap. A 1.5kW oil-filled radiator running continuously for an hour therefore costs 1.5 × 26.11p = 39.2p at most. The interesting part — and the reason oil-filled radiators feel cheap to run — is that they rarely run continuously, as we’ll see below.

Running costs by size: maximum vs typical

The “typical” column assumes the element is actually drawing power for about 60% of the time — a reasonable mid-range figure for a thermostat-controlled radiator holding a room at temperature. Your own duty cycle could be higher in a cold, draughty room or lower in a snug one.

What a thermostat duty cycle actually means

An oil-filled radiator works by heating a sealed reservoir of thermal oil, which then radiates warmth from its metal fins. Once the oil — and the room — reach the temperature you’ve set, the thermostat switches the element off. Crucially, the hot oil keeps giving off heat while the element is drawing no power at all, and the thermostat only clicks back in when the temperature drops. The share of time the element is actually on is called the duty cycle.

Worked example: a 1.5kW radiator holding a bedroom warm for a four-hour evening at a 60% duty cycle uses 1.5 × 4 × 0.6 = 3.6kWh, which costs 94p. Do that every evening for a month and you’re at around 108kWh, or £28.20 — well under half the £47 you’d estimate from the maximum-power figure alone.

Oil-filled vs fan heater: is one cheaper?

Per unit of heat, no — both are resistance heaters, so every kWh costs 26.11p whichever box it comes out of. The practical difference is behaviour: a fan heater gives fast heat and is either on or off, while an oil-filled radiator warms up slowly, holds heat, cycles gently and is silent. For a room you occupy for hours at a time, the steady cycling and retained heat usually mean a lower bill for the same comfort; for a ten-minute blast, the fan heater wins because you’re not waiting for oil to warm up. Our full portable heater comparison puts all the types side by side.

Choosing the right size — and keeping the cost down

• 0.5–1kW suits a desk, box room or small bedroom; 1.5kW an average bedroom; 2–2.5kW a living room. Oversizing wastes money, undersizing means the element never switches off.
• Set the thermostat to the lowest comfortable level — each notch down shortens the duty cycle and directly cuts the bill.
• Use the built-in timer (or a plug-in one) so the radiator warms the room just before you need it, not all day.
• Keep doors closed and sort draughts first: better insulation and draught-proofing reduce how hard any heater has to work.
• Remember the wider picture — heating one room electrically is fine, but whole-home electric heating at 26.11p/kWh is roughly three times the price of gas heat, as our guide to the price cap explains.

Oil-filled radiator vs gas central heating

The comparison every electric-heater owner should know: gas costs 7.33p per kWh at the current cap, and through a boiler running at around 85–90% efficiency a kWh of delivered heat comes out at roughly 8.5–9p — about a third of the 26.11p you pay for electric resistance heat. An oil-filled radiator is therefore a sensible tool for one room you use a lot, a home office, or shoulder-season evenings when firing the whole heating system feels excessive — and an expensive mistake as a whole-home heating strategy. If you find yourself running two or three of them daily through winter, the money is telling you to look at the heating system itself.

One quality-of-life upgrade worth having: a cheap plug-in timer or smart plug. Oil-filled radiators take 15–20 minutes to warm up, so scheduling one to switch on shortly before you get up — or before you sit down to work — gives you fan-heater convenience at oil-filled running costs, with no element left running in an empty room.

FAQs

Is it cheaper to leave an oil-filled radiator on low all day?

Usually not. Heat leaks out of a room at a rate that depends on the temperature difference, so keeping a room warm all day means paying for all-day heat loss. Heating the room only when you use it — ideally on a timer — almost always uses less energy overall.

How much does an oil-filled radiator cost overnight?

A 1kW model holding a bedroom at temperature on a 60% duty cycle for eight hours uses about 4.8kWh — around £1.25 a night at the current cap. An electric blanket does the same comfort job for under 10p, so it’s worth considering for sleeping hours.

Do oil-filled radiators use less electricity than other electric heaters?

They don’t create heat more efficiently — no plug-in heater does — but their thermostat cycling and heat retention mean they typically draw power for less of the time to hold the same temperature, which is why real-world running costs often come in lower than the nameplate wattage suggests.