What it costs to run a space heater

An electric space heater, whether a fan heater, a convector or an oil-filled radiator, is handy: it warms up straight away and heats only the room you are in. But its power is high, often 1,000-2,000 W, and each kWh of electric heat usually costs more than heat from a gas boiler. This calculator estimates the heater's annual cost and compares it with the cost of the same heat from gas.

It works in any currency: enter the prices from your bills.

How the calculation works

• Energy: power × hours per day × share of time heating × days of use.
• Cost with the heater: resistance heaters turn almost all the electricity into heat, so each kWh used is a kWh of heat.
• Same heat from gas: the same kWh of heat, at the gas price divided by the boiler efficiency.
• Ratio: how many times more a kWh of electric heat costs than a kWh of gas heat.

Hours make the cost

A 1,500 W heater, thermostat heating 70% of the time, 120 days, electricity at 0.30 and gas at 0.10 per kWh with a 90% boiler:

The gas comparison covers only the heat produced: a boiler usually heats the whole home, a space heater one room. That is why a space heater can save money if it lets you keep the central heating off when you need warmth in just one room.

How much the energy price matters

Same heater, 5 hours a day, gas at 0.10 per kWh:

The reading bands

• Ratio up to 1: electric heat costs no more than gas heat.
• Up to 2: worth it for warming one room for a few hours, not as main heating.
• Up to 3: worth it only if it lets you turn off the heating in the rest of the home.
• Above 3: use only for short periods and in small rooms.

What about a heat pump?

An air conditioner in heating mode or a heat pump typically produces 3 or more kWh of heat for every kWh of electricity. With the same electricity it delivers far more heat than a resistance heater: if you have one, use it before the space heater.

Limits of the calculator

The on-time share is an estimate: it depends on the thermostat, insulation and outdoor temperature. The calculator does not compare the heater with the real cost of heating your whole home, only the cost of each kWh of heat. Use heaters with care: keep them away from curtains and furniture, do not cover them and avoid undersized extension leads.

Frequently asked questions

How much does a space heater cost to run?

A 1,500 W heater on 5 hours a day, with the thermostat heating 70% of the time, uses about 630 kWh over 120 days: about 189 at 0.30 per kWh.

Is a space heater cheaper than gas central heating?

Per kWh of heat, usually not: with electricity at 0.30 and gas at 0.10 with a 90% boiler, electric heat costs about 2.7 times as much as gas heat.

So a space heater never pays off?

It can, if it heats one room for a few hours and lets you keep the heating off in the rest of the home.

Do oil-filled heaters use less?

Not for the same heat output: all resistance heaters turn electricity into heat in a similar way. What changes is how they spread it.

What about a heat pump?

It typically produces 3 or more kWh of heat per kWh of electricity, so it delivers far more heat than a space heater for the same consumption.

How do I find the gas price per kWh?

On your bill, or by dividing the price per cubic metre by the calorific value given by your supplier (often about 10 kWh per m³).

Why enter the on-time share?

Because the thermostat switches the element off when the room is warm: the heater does not always draw its rated power.

How do I measure real use?

With a plug-in energy meter for a few days.

Is it safe to leave it on overnight?

Follow the manufacturer's instructions: keep it away from fabrics and furniture, do not cover it and do not use undersized extension leads.