As the cold sets in, the same question comes up in every shop aisle and search bar: which electric heater warms a room best for the least money? The answer catches most people out, because the type you buy matters far less than how you run it. Whether you need a main source of warmth or just a top-up in one room, it pays to know what really separates a convector, a panel heater and an oil-filled or ceramic radiator before you spend a penny.
No electric heater is cheaper to run than another at the same wattage
This is the fact that upends most buying decisions: every plug-in electric heater turns 100% of the electricity it draws into heat. A 1,500W convector and a 1,500W oil-filled radiator, left on for the same length of time, use exactly the same energy.
The technology does not lower what you consume: it only changes how the heat spreads around the room and how long it lingers. A 1,500W heater running four hours a day draws 6kWh, which is about £1.57 a day at a unit rate of 26.11p per kWh. Whether it cost £30 or £600, that figure does not shift by a penny.
To see what a heater really costs you across the winter, start from your own room: its power, the hours you run it, the days of cold weather and your unit rate.
Convector, panel and oil-filled: match the heater to the room
Each type has a room where it earns its place. A convector or fan heater warms the air fast and lets it cool just as fast: it dries the room, leaves the ceiling warmer than the floor and only makes sense where you stay a short while, such as a hallway or a spare room.
A panel heater gives quick, direct warmth and suits a room used on and off, like a bathroom or a study. An oil-filled radiator is a cheap middle ground: it holds heat better than a convector, but warms up and cools down slowly. Night-storage heaters are a separate case, tied to off-peak tariffs such as Economy 7.
An oil-filled or ceramic electric radiator stores heat in a fluid or a solid core and releases it gently, holding a steady temperature with no spikes or dips. That makes it the sensible choice in rooms you sit in for hours, such as a living room or bedroom. In practice, a well-kitted home mixes all three rather than fitting the priciest model in every room.
The real gain from thermal mass is one degree lower
If a heat-storing radiator does not run cheaper at the same wattage, where is the benefit? In the steadiness. An even warmth with no swings lets you feel just as comfortable with the thermostat set one degree lower, and every degree off your heating trims consumption by roughly 7%.
On a home using around 4,800kWh a year for heating, that one degree is about 336kWh, close to £88 saved over a season at 26.11p per kWh. That is where a pricier oil-filled or ceramic model earns its keep, but only in a room used for many hours a day; in a space you pass through for ten minutes, the stored heat never gets the chance to pay off.
Good to know: dropping the thermostat from 20 to 19°C is not something you feel on your skin, but you see it on the bill. It is the single change with the best effort-to-saving ratio, whatever heater you own.
Watch out for cheap heaters dressed up as "inertia" radiators
The word "inertia" sells, and plenty of budget convectors borrow it without the substance behind it. A genuine heat-retaining radiator has real mass: it is heavy and it names a solid core in ceramic, stone or cast iron, or a heat-transfer fluid. If a unit is feather-light, very cheap and only warm while it is switched on, it is a convector dressed up as an inertia radiator.
Before you pay, these are the signs that tell a real model from one trading on the label:
- It is noticeably heavy: the mass that stores the heat can be felt the moment you lift it.
- It names the storage material: ceramic, stone, cast iron or a heat-transfer fluid, stated on the spec sheet.
- It has a thermostat accurate to the degree with a built-in timer.
- It keeps giving off heat after switching off, a sign the core is releasing stored warmth.
- It weighs almost nothing: there is only an element and thin metal inside.
- It names no storage material, just the word "inertia" on the box.
- It has a basic dial, with no timer or programming.
- It turns cold within moments of switching off.
The controls matter as much as the heater
A high-end radiator with a manual dial will, on your bill, heat worse than a well-programmed convector. How you control the heat does more for your bill than the technology you pick: the point is to warm the right rooms, only in the right hours.
Three levers make the difference, in order of impact:
- A programmable thermostat that switches between heating and holding: the single biggest lever on your bill.
- Room-by-room control, with thermostatic valves or separate thermostats, so you never heat empty rooms.
- Turning the temperature down overnight and when out, rather than switching everything off and reheating from cold.
Getting the wattage wrong is the costliest mistake
An underpowered heater runs flat out and never quite warms the room; an oversized one wastes energy and overshoots. Size it to the room, not to guesswork: the figure depends on volume and insulation, not floor area alone.
As a rough guide, allow around 100 watts per square metre for average insulation and closer to 70 watts for a well-insulated room, adding a little for large windows; for the same floor area, insulation alone can shift the power you need by up to 50%. That is why, before paying for a top-of-the-range model, it is worth putting the money into insulation first. To see where heating sits among your costs, start with our guide to appliance running costs, brush up on what a kWh really is and check how the unit rate on your tariff shapes every hour of use.
- Three things to check before you pay
- How many hours a day you use the room: only long use justifies paying for thermal mass.
- What controls it carries: a programmable thermostat, not a plain dial.
- Power worked out from volume and insulation, not guessed from floor area.