Fan heater: how many watts per square metre?

Rule of thumb: watts per square metre

For short-term top-up heating of a single room, allow roughly 60 to 100 watts per square metre, depending on insulation, ceiling height and outside temperature. In well-insulated new builds 60 W/m² is often enough; in older buildings with high ceilings or poorly insulated windows you should rather allow 100 W/m².

This gives the following for typical rooms:

• Small bathroom (4 to 6 m²): 400 to 600 W is enough for quick warming up; a 1,000 W appliance on a low setting is ideal here.
• Home office / small room (10 to 12 m²): 800 to 1,200 W. A typical 1,500 W fan heater with a thermostat covers that easily.
• Living room (18 to 25 m²): 1,500 to 2,000 W as top-up heating. As the sole heating for a room like that, though, electricity is hardly economical (more on that below).

Important: these values apply to topping up and quick warming, not to permanent heating through the whole heating season. A fan heater is a sprinter, not a marathon runner.

What a fan heater really costs per hour

The running cost depends on only two quantities: the actual power consumption and the electricity price. At an average electricity price of 35 cents per kWh (as of 2026), one hour at full load costs:

• 1,000 watts: 1.0 kWh × €0.35 = €0.35 per hour
• 1,500 watts: 1.5 kWh × €0.35 = €0.53 per hour
• 2,000 watts: 2.0 kWh × €0.35 = €0.70 per hour

That sounds manageable at first. But if a 2,000 W appliance runs for eight hours on a cold day, that is €5.60 in a single day, or around €170 a month. That is exactly why a fan heater is so expensive as permanent heating: per kilowatt-hour, electricity costs about three to four times as much as gas.

The trick lies in the thermostat and Eco mode: good appliances do not run continuously at full load but cycle down as soon as the target temperature is reached. Averaged over an hour, a 1,500 W appliance with a thermostat then often draws only 600 to 900 W effectively, which halves the cost compared with continuous operation.

When electric heating pays off, and when it doesn't

A fan heater plays to its strengths exactly when heat is wanted fast, in one spot and briefly:

• The bathroom in the morning: 10 minutes of preheating before the shower, cheaper and faster than firing up the central heating for one room.
• Shoulder season (autumn/spring): when the central heating is still off but a single room should be warm for once.
• Home office in an otherwise unused room: warm only the workspace instead of the whole flat.

A fan heater is not economical, however, as a replacement for the central heating over the whole season or for heating large, poorly insulated rooms. Here you pay extra through the electricity price.

Ceramic, thermostat and Eco: what matters for efficiency

Three features decide whether a fan heater uses its energy economically:

• Ceramic heating element instead of heating wire: ceramic releases heat more evenly, does not overheat and is safer. Almost all recommendable models today use ceramic (PTC).
• Thermostat: regulates the output according to room temperature and prevents expensive continuous heating. A simple dial is enough; digital with a target temperature is more convenient.
• Eco mode: automatically selects the lowest setting that holds the target temperature. This is where real consumption is decided: an appliance such as the Dreo Atom 316 with Eco mode and 34 dB operating noise heats much more economically than a simple 2,000 W fan heater without regulation.

Which appliances do this well is in the fan heater comparison. The direct efficiency showdown of quiet/economical against tower comfort is shown in the head-to-head Dreo Atom 316 vs De'Longhi HFX65.

Fan heaters in the bathroom: IP protection is a must

In the bathroom a safety rule applies that many overlook: the appliance must be splash-proof, recognisable by protection rating IP21 or higher. A normal room fan heater without an IP marking does not belong in the bathroom, because water and 230 volts are a dangerous combination.

Appliances designed for wet areas, such as the Rowenta Instant Comfort Aqua (IP21, 2,400 W), heat quickly and are protected against splashes. The difference between “bathroom and room” is explained in the head-to-head Rowenta SO6511 vs Dreo Atom 316. Rule of thumb: an IP21 appliance for the bathroom, a quiet, economical one without IP protection for the bedroom, never the other way round.

How to heat most economically

• Door closed: heat only the room in use, not the hallway as well.
• Set the thermostat moderately: every degree lower saves roughly 6 % of energy.
• Run it only when someone is there: a fan heater warms up in minutes; continuous operation in empty rooms is money thrown away.
• Size it properly: better a 1,500 W appliance with a thermostat in a small room than a 2,000 W appliance on permanent full load.

Frequently asked questions: fan heaters in the bathroom

Can you use a fan heater in the bathroom?

Yes, but only appliances with protection rating IP21 or higher (splash-proof). A normal room fan heater without an IP marking does not belong in the bathroom. In addition, the prescribed safety distance from the shower and bath must be kept: no fan heater may go directly in the splash zone.

What IP protection rating does a fan heater need for the bathroom?

At least IP21: the first digit (2) stands for protection against foreign objects, the second (1) for protection against vertically falling drips. Close to the shower, IP24 (splashing water from all directions) is safer still. Appliances with no IP rating at all are approved only for dry rooms.

How many watts does a fan heater need for the bathroom?

For a typical bathroom of 4 to 6 m², 400 to 600 watts is enough for quick warming up. In practice you use a 1,000 to 2,000 watt appliance and preheat only briefly before the shower, 5 to 10 minutes on the right setting, instead of running permanently at full load.

What does an hour of fan heater cost in the bathroom?

At 35 cents per kWh (German electricity price), a 1,000 W appliance costs €0.35 and a 2,000 W appliance €0.70 per hour at full load. Because in the bathroom you usually only preheat for 10 to 15 minutes, the real cost per use stays in the low cent range, so a fan heater is exactly right here.

Verdict

Allow 60 to 100 watts per square metre for quick top-up heating and use the fan heater selectively rather than as permanent heating. An hour at full load costs €0.35 to €0.70 depending on output, and considerably less with a thermostat and Eco mode. For the bathroom IP21 is a must; for the bedroom a quiet, adjustable appliance counts. Which model suits your room is in the fan heater comparison.