Best Oil-Filled Radiators UK [2026]: Running Costs and Smart Options

You work from the spare room, the rest of the house is empty all day, and firing up the whole central heating system for one person feels wasteful. An oil-filled radiator can heat just that room — as long as you know what it really costs.

I've compared these from manufacturer specifications. I haven't tested them in my own home.

Pick the De'Longhi Dragon 4 (TRD40820T) for a well-known 2kW radiator with a timer and heat settings. Pick the Mill Gentle Air Wi-Fi if you want app scheduling and Matter support.

Under the October 2026 cap, electricity averages 26.32p per kWh and gas 7.97p. That makes every unit of electric heat roughly three times the cost of gas heat. A 2kW radiator at full power costs about 53p an hour. Its thermostat will cycle it on and off once the room is warm, so the real cost depends on the room and the weather.

That's why these heaters make sense for one room, for a few hours, with the central heating turned down elsewhere — not as a replacement for gas central heating.

De'Longhi Dragon 4 TRD40820T — best standard model

De'Longhi lists a 2kW maximum with lower settings of 900W and 1,100W, an eco function, a manual timer, cord storage and castors. The Dragon range is a long-standing UK bestseller.

Choose it if: you want a simple, well-supported radiator. Think twice if: you want to control it from your phone.

Check current price of the De'Longhi Dragon 4

Mill Gentle Air Wi-Fi 1500W — best smart option

Mill lists 1,500W with settings of 600, 900 and 1,500W, a recommended room size of 18–22m², Wi-Fi control through the Mill app, Matter compatibility and a 5-year warranty.

Choose it if: you want schedules and room temperature control from an app. Think twice if: your room is large — check Mill's room-size guidance first.

Check current price of the Mill Gentle Air Wi-Fi

*At 26.32p per kWh. Thermostat cycling usually reduces real-world cost.

Close the door, use the lowest setting that keeps you comfortable and set a timer so it doesn't run when you've left the room. Turn the radiator valve down in that room so the central heating isn't fighting it — smart radiator valves make that automatic.

Plug heaters directly into a wall socket, not an extension lead, and keep them clear of curtains and drying clothes. That last one is the point I'd underline from 30 years in electrical engineering: a 2kW heater is a big, continuous load. Never cover a heater.

• De'Longhi UK: Dragon 4 TRD40820T

• Mill: Gentle Air Wi-Fi Oil Filled Radiator 1500W

• Ofgem: October–December 2026 price cap rates

*Researched October 2026 from manufacturer specifications, official guidance and independent UK sources; we do not test products in our own home. Prices change often — always check the current price before buying. This article contains affiliate links — see our disclosure.*