Space heater running costs: how to heat a small room without a scary bill
Heating the whole house for the one room you actually occupy is the most expensive way to stay warm. A well-chosen space heater does the opposite: it heats the spot you're in, while you're in it. Here's how to work out the real cost, pick the right wattage and avoid the classic mistakes.
The real cost per hour: 10-second math
The formula fits on one line: power (kW) × hours of use × price per kWh. A 1,200 W heater running 3 hours per evening at €0.25/kWh costs 1.2 × 3 × 0.25 = €0.90 per evening. Roughly €27 a month — for a genuinely warm room, during the hours you're actually in it.
The comparison that matters: raising central heating by 2 degrees for the whole home typically costs 3 to 5 times more than spot-heating the one occupied room. A space heater isn't cheap 'by nature' — it's cheap because it heats small and short.
The rule that follows: a space heater is a complement, room by room, session by session. Leave it running 24/7 in a large, badly insulated living room and the math turns against you.
Sizing the wattage to the room
The standard rule of thumb: about 100 W per m² (roughly 10 W per sq ft) for a normally insulated room. A 10–15 m² office or bedroom needs 1,000–1,500 W — no point going bigger, an oversized unit just cycles constantly without adding comfort.
Ceramic (PTC) technology has a concrete advantage in small spaces: it reaches temperature in tens of seconds and self-regulates — the ceramic element naturally draws less power as it approaches its target temperature. That makes it the right pick for short, repeated sessions, which is exactly the desk/bedroom use case.
Since 2018, EU ecodesign rules (ErP) require electric space heaters to have electronic temperature control. An electronic thermostat isn't a gimmick: it's what stops the unit heating beyond what's needed — and it's legally required for sale in Europe.
Safety: the two non-negotiable protections
Overheat cut-off and tip-over cut-off. Both must be stated explicitly in the spec sheet. A heater on a desk or near a bed without tip-over protection is a hazard, not a saving.
Usage rules are the same whatever the device: never covered, never against fabric, never on an already-loaded power strip (1,200 W is half of what a standard strip tolerates), and no extended unattended running.
The mistakes that cost money
Heating a room with open windows or terrible insulation: the unit runs flat-out non-stop and costs balloon. Five minutes of full-open-window airing, then windows shut, beats a permanently cracked-open window.
Under-sizing 'to save money': a 500 W unit in a 20 m² room runs forever without reaching temperature — you pay without comfort. The right wattage used for less time always wins.
Ignoring placement: floor or desk level, airflow pointed at you, not at the door. A fan heater's warmth is directional — that's its strength at a workstation, provided you aim it.