Heat pump running costs vs gas, oil and electric heating

How we worked it out

We take the heat a typical home needs in a year, divide by the efficiency of each system to get the fuel used, then multiply by the price per kWh. A heat pump with a SCOP of 3.5 needs 1 kWh of electricity for every 3.5 kWh of heat.

What changes the result

• Your tariff: a smart or night rate tariff can cut heat pump running costs by a fifth or more
• How well it was designed: an oversized or badly set up heat pump runs less efficiently
• Flow temperature: every degree lower saves a little more
• Fuel prices: oil and gas prices swing more than electricity

Why some heat pumps cost a fortune to run

Homeowners who say their bills went up almost always describe the same few problems. None of them are faults of heat pumps as such; they are faults of the design or the house.

• Too big: an oversized unit switches on and off all day instead of running gently, which wastes energy
• Too small: an undersized unit can't keep up on cold days, so the electric immersion or backup heater does the work
• A leaky house: poor windows, doors or insulation let heat out as fast as the pump makes it
• Flow temperature set too high: running at 55°C to 60°C instead of 35°C to 45°C can cut efficiency by a third
• The wrong tariff: heating and hot water on day rate instead of a night or smart tariff

How to avoid it

• Insist on a room by room heat loss calculation before you accept a quote; the unit size should come from it
• Ask what flow temperature the system is designed for, and get it in writing
• Ask the installer to set up the controls with you and show you the running data after the first month