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Heat Pumps

Heat Pumps use the free heat energy from the earth, water or air and draw it into the building to provide space heating and, in some cases, to pre-heat hot water. They can also be used to cool the house in summer. They work like a fridge – liquid in looped pipes extracts heat from the earth, water or air, and draws it into your house to heat it via radiators or under-floor heating. They need electricity to pump the heat, but for every unit of electricity used, optimally 3-4 units of heat should be produced.

Ground source heat pumps are most efficient because the temperature under ground remains more or less constant all year round. In contrast, the efficiency of air source heat pumps will fall at extremes of outside temperature, for instance in very cold or freezing conditions. However, both types can achieve considerable savings on heating bills in comparison to heating with electricity, oil or LPG, for properties off the gas grid.

What are the costs and savings?

The cost of heat pump installations varies enormously depending on the technology, type and size of house, and the requirements of the residents. One key factor is whether the system is used only for space heating, or to provide hot water as well. Air source heat pumps typically fall in the range of £6000 to £10,000 installed, whereas ground source systems can cost anything from £13,000 to £20,000 installed.

The Energy Saving Trust gives more details on costs and benefits of both ground source heat pumps (GSHPs) and air source heat pumps (ASHPs). Ground source heat pumps and certain air source heat pumps are eligible for tariff payments under the Renewable Heat Incentive scheme. Typical annual payments are in the range £2500-3500 for GSHPs, and £800-1000 for ASHPs.

Important points

  • Heat pumps can be installed in existing houses, even without much space outside. However, if there is not much outside space the loop must go deep into the ground rather than horizontally, or an air source heat pump may be more suitable.
  • The ground will need to be suitable for digging a trench or borehole.
  • The existing central heating pipes and radiators can be used to circulate the heat, but under-floor heating is better as it works more efficiently at a lower temperature.
  • Solar or wind power may be used to generate the electricity needed for the pump. If not, choose the best electric tariff for lowest running costs, for example economy 7.
  • An accredited installer will be able to provide more detailed advice.
  • Heat pumps are an attactive option for properties off the gas grid, or for new-build homes.
  • If you are building a new house or extension or other major building works requiring excavation equipment, this can make the installation of a heat pumpgshp loop more cost-effective.
  • Make sure your property is well insulated to lower your need for space heating and make the system more effective.
  • Heat pumps will make some noise, so take care this won't disturb you or your neighbours.
Image courtesy of greenspec.co.uk

Carbon savings

According to the Energy Saving Trust, a heat pump uses only one-third the amount of energy that would be used by an average gas boiler or oil-fired boiler to produce the same amount of heat. However, the electricity it requires is more carbon intensive than gas or oil. Hence, a heat pump produces about 9% less carbon than a gas boiler, and 28% less than an oil boiler per unit of heat produced.

  • Fitting heat pumps to all 5 million off-gas properties could save 10 million tonnes of CO2 per year.