Oil-Filled Radiator vs Convector Heater: Which Should You Buy?

Every plug-in electric heater converts essentially all of its electricity into heat, which the Energy Saving Trust confirms across oil-filled, convector, panel and fan types. There is no efficiency difference to shop for. At the current price cap rate of 26.32p per kWh, the maths is fixed by wattage alone:

"Flat out" is the key phrase. A heater with an accurate thermostat spends much of each hour switched off once the room is up to temperature, so the control quality decides your real bill, not the heater type. This is also why the oil-filled radiator feels cheaper over a long evening: its hot oil keeps radiating through the off part of each cycle, so the element draws power for fewer minutes per hour to hold the same comfort.

An oil-filled radiator runs its element inside a sealed reservoir of oil, which heats the fins, which warm the room by radiation and gentle convection. The oil is a heat store: expect 15 to 20 minutes before the room notices, and warmth that outlasts the thermostat clicking off. The surfaces get properly hot, the heat feels like a traditional radiator's, and the whole thing is silent.

A convector passes air directly over an exposed element: cold air in at the bottom, warm air out of the top grille, a circulating current within a couple of minutes. Nothing stores heat, so output stops dead at switch-off, but nothing has to warm up either. Panel convectors are also slim and light, often wall-mountable, where an oil-filled unit is a chunky thing on castors.

Both are silent, which is the shared advantage over fan heaters. The practical difference is the duty cycle: the oil-filled unit suits hours of steady occupancy, the convector suits warm-this-room-now moments. Neither is "warmer" at the same wattage; they just deliver the same watts on different schedules.

• The home office. Six hours at a desk is exactly the steady, thermostat-cycled load the oil reservoir is made for, and the silence matters on calls. This is the single biggest reason these sold out in recent winters.
• Living rooms in the evening. Switch it on when you sit down and the room holds an even, radiator-like warmth without the dry blast of moving air.
• Anywhere you want background heat for long stretches. The retained warmth smooths out the on-off cycling, so the temperature swings less than with a convector in the same room.
• Toddler-adjacent rooms, with a caveat. No exposed element is a point in its favour, but the fins still get hot enough to hurt; models with a cool-touch outer cage are the answer where small hands roam.

One myth to retire while we are here: the oil is sealed for life and is never refilled or replaced. It is a heat-transfer fluid, not a fuel. Our oil-filled radiator guide ranks the current picks, with timers and thermostats weighted heavily, because controls are where the savings are.

• Rooms used briefly and unpredictably. A bedroom for an hour before sleep, a spare room when guests land. Minutes-fast warm air with no warm-up tax.
• Scheduled heat. The better convectors and panel heaters carry digital thermostats, 7-day timers, sometimes wifi, so the room warms for 7am and gives up at 9 when you leave. An oil-filled unit on a timer still needs its warm-up window factored in.
• Tight spaces. Slim, light, often wall-mountable: a panel convector disappears against a wall where an oil-filled radiator eats floor.
• Taking the chill off quickly. If the complaint is "this room is freezing right now", the convector answers in two minutes, which no amount of oil thermal mass can.

Our convector heater guide covers the picks, and leans hard on models with proper thermostats and timers for exactly the runtime reasons above.

The rules are the same for both types, and worth stating because winter heater fires are depressingly regular fire-service work.

• Wall socket only for big heaters. A 3kW heater sits at the very top of what a UK 13A socket delivers, around 2,990W, and Electrical Safety First guidance is that high-wattage heaters plug straight into the wall, never a multi-way extension lead.
• Nothing draped over, ever. Clothes on a heater are a fire risk on a convector and a scorch-and-moisture mistake on an oil-filled unit. If the washing is the problem, our indoor drying guide has the 5p an hour answer.
• Keep a metre clear. Curtains, bedding and sofas stay out of the heat path, and the heater stands on a hard level floor, not deep carpet pile against fabric.
• No portable heater in the bathroom. Plug-in heaters of any type do not belong there; bathroom heating must be a fixed, suitably IP-rated unit installed to the BS 7671 bathroom zone rules.
• Unattended running: use the thermostat, mind the room. Both types are designed to cycle on a thermostat, which is far safer than running flat out, but anything with a hot surface deserves a clutter-free space and a working smoke alarm on the same floor.

Before either heater, a reality check from our cheapest way to heat a room guide: if the job is keeping one or two people comfortable rather than warming air, a heated throw does it for 2 to 3p an hour, where a 2kW heater of either type costs 53p flat out. Over a winter of evenings that is the difference between pounds and pennies.

The honest combination for a cold room this winter is both layers: the blanket as the default for sitting still, with the right heater, oil-filled for the long-haul rooms, convector for the quick ones, deployed when you need actual warm air for guests, work or a freezing morning. Buying the heater second, once you know which rooms genuinely need air heated, usually means buying one heater instead of three. Our electric blanket guide covers the 3p an hour layer.