To be environmentally beneficial, the whole heating system must be properly specified and the house very well insulated (to a level above that specified by current UK Building Regulations). You can vastly improve the efficiency of your existing property with simple energy conservation measures - see our Energy Conservation section for advice.
The efficiency of a heat pump is given by its Coefficient of Performance (COP). A system operating at COP3 will give out 3 units of heat energy for each unit of electricity used. However, the COP excludes factors such as any auxiliary electric heater or an immersion heater used to 'top-up' heating or hot water, or electricity for pumps and fans. It is more useful to look at overall system efficiency – total heat output compared to total electricity use across different weather conditions. A Seasonal Performance Factor (SPF) can be used for this, so you may see this term quoted as well.
It is very important to get the SPF or COP as high as possible, as most grid electricity is still generated from fossil fuels (coal & gas) or nuclear power, at efficiencies of only 30 to 40%, so you’ll need a very good COP to outweigh this. A heat pump with poor seasonal efficiency can result in higher carbon dioxide emissions than a modern gas, oil or LPG boiler. Electricity generation also causes other forms of pollution: sulphur & nitrogen oxides (that cause acid rain), particulates, mining impacts, and nuclear waste.
An Energy Saving Trust field trial of 83 heat pumps in the UK found a wide variance in performance - only a few reached a COP of 3 or more. The average COP for air source heat pumps was 2.1, while the average for ground source systems was 2.3. Many were early installations, and as installers gain experience, performance should improve. To avoid a low COP, ensure that a home is well-insulated, has a low-temperature heating system and good heating controls, and that the ground loop or air-source unit has been adequately sized. See other questions and our information sheet for advice.
You can sign up for a 'green tariff', and have your electricity use allocated to renewable sources such as wind or hydro power. This is an excellent way to help promote the growth of the renewable energy industry, but it’s not a green light to use loads of electricity! Doing so will increase overall electricity demand, and until more renewable energy technologies are ready, this will increase the use of fossil fuels and nuclear power.
If you have a stream that would be suitable for a micro-hydro system, then a renewably-powered heat pump could be feasible and beneficial. See our Micro-Hydro page for initial advice on this technology.
A heat pump contains about 2 kilos of refrigerant, usually hydrofluorocarbons (HFCs). These are potent greenhouse gases (about 1600 times more powerful than carbon dioxide) and a leak during or after the system’s life will have a damaging impact. Some suppliers use hydrocarbon refrigerants such as R290 or R600a (propane & isobutane); these will have a much lower impact if accidentally leaked.