Different systems use different amounts of energy to deliver the same warmth. Efficiency, the temperature you set, how long you run the system and your home’s insulation all matter.
Compare the energy used to deliver heat
An air conditioner moves heat rather than creating it directly, so it can deliver several kWh of heat for each kWh of electricity it uses. A gas boiler loses some energy as it burns fuel. A plug-in electric heater delivers about one kWh of heat for each kWh of electricity.
An example
This illustration compares energy input for one kWh of heat. Actual use depends on each system’s efficiency, your set point, run time and insulation.
| Heat source | Energy input for 1 kWh of heat |
|---|---|
| Plug-in electric heater | About 1 kWh of electricity |
| Gas boiler at 90% efficiency | About 1.1 kWh of gas |
| Air conditioner with a SCOP of 4 | About 0.25 kWh of electricity |
These figures describe energy use, not a bill. Your tariff decides what that energy costs; ask your supplier for the rates that apply to your home.
Heat the room, not the house
Central heating usually warms the whole house at once. An air conditioner warms the room you’re in. Heating fewer rooms can reduce energy use when you spend most evenings in one or two rooms, depending on your set point, run time and insulation.
Where central heating still helps
- Heating every room at the same time
- Hot water: an air conditioner doesn’t make any
Many homes use both: air conditioning for the rooms they live in, and the boiler for hot water and the coldest days. Compare their energy use under your own conditions before deciding how to run them.