The thermal store suits the average 3 bedroom semi' and the air source heat pump is the ideal technology for a house without a large garden. Because it saves having to have an expensive and disruptive bore hole. Air is not quite as efficient as ground source but that small loss in efficiency is compensated for by the far easier installation. For a great deal of the time the air temperature outside exceeds that of underground temperatures but of course it drops dramatically at night time just when you need it most. Here ground source wins because the temperature below ground hardly fluctuates and you can run the heat pump day and night at a very steady temperature.

With air source you are better off running the system to build up a heat bank during the day. The thermal store has a very limited capacity so it is better to run the under floor heating even when the homeowner isn't in because you can then build up the heat store in the concrete floor as well as the Gledhill unit.

Self Builder went to a new build site just down the road from Stonehenge to see the installation of six Gledhill/Mitsubishi air source heat pumps. The installation was being carried out by Ayres plumbing and Heating of Amesbury for Ankers and Rawling property developers. Ayres has a great deal of experience in renewable's and sees air source heat pumps as the future.

The original spec for the houses was for oil boilers but there were issues with the oil storage which due to environmental and health and safety considerations is now a lot more exacting that it used to be. The heat pump option turned out to be the simplest option because it requires nothing more than an electricity supply. It will also show significant savings on running costs and place the houses a very low carbon rating.

Director and Technical Consultant John Ayres met me on site to show us how well the units work. It doesn't matter how much you read on this subject the epiphany moment is when you put your hand on the hot flow pipe coming out of the heat pump. You then become a true believer.