Electric heat pumps (aka air conditioners) are very efficient machines. They achieve this efficiency by capturing heat in the air outside your home and transferring it to the inside - or, in a heat wave, transferring unwanted heat inside the house to the outside. A typical domestic heat pump has an energy efficiency rating (EER) of between three and five, meaning that for every one kilowatt of electricity it consumes, it transfers three to five kilowatts of heat.

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Below is a comparison with other forms of heating.