What does an electric boiler cost to run?

Work it out from three numbers

Daily cost = average power used (kW) x hours of heating x your price per kWh. The first number is the one that takes thought, because an Advance Appliances Eglow does not run flat out all the time.

The Eglow is fully modulating. It only runs at full output at start-up, then uses a share of its rated power to hold the temperature. The installation guide adds that it soft switches on start-up, which reduces the load on the household electricity supply.

Advance's worked example

Advance's own example assumes heating for two hours in the morning and six in the evening, with a 6kW Eglow averaging 50% of its output after start-up:

• 6kW x 50% = 3kW average
• 3kW x 8 hours = 24kWh a day
• 24 x your price per kWh = your daily heating cost

The 50% is Advance's assumption for the example. The real share depends on the home, the weather and the thermostat setting, so treat the result as a guide and use your own tariff and hours.

The same sum works for the bigger models. A 9kW or 12kW Eglow is sized for more radiators, so it has more heat to supply; see how many radiators an Eglow will run.

All the power becomes heat

Advance's data sheet says the Eglow converts all its power to heat, and it needs no maintenance in ordinary use.

Keeping the cost down

• Use off peak supplies where possible; the installation guide recommends it to reduce running costs.
• Run it from a programmer and room thermostat, which Part L of the Building Regulations requires anyway, and heat only the hours you need.
• Set the room thermostat at a comfortable level; the guide suggests around 20°C, in a room with a radiator locked open.
• For hot water, Advance recommends an independent electric or solar cylinder for the best efficiency.
• For an apartment wanting heating and hot water from one unit, the ECO ECB 210 electric combi stores heat from off peak electricity and runs four to five radiators.

Adding a free heat source

On a self build in Morayshire, Rob Rankin paired a 12kW Eglow with an Advance multi fuel thermal store and a wood burner, using wood as free fuel to cut his electricity bills. See how that set-up works in thermal stores with a wood burner.