Despite the fact that it was sleeting the water flowing from the heat pump to the thermal store was hot within minutes of switching on and everyone, including the plumbers kept sneaking up to the units to place their hand on the pipe, which in the normal course of events would have been insulated. Even among seasoned building professionals there was clear (somewhat childish) delight to see these units extracting heat from air which we would normally regard as cold. 'How is it possible?' we heard people saying to each other.

Another reason we wanted to see the units working was concerns about noise. If these units are mounted on the patio or near the neighbour's then noise is a consideration. They turned out to be exceptionally quiet. Nothing like the air-con units you encounter on holiday. There are units which are placed in the loft to recover heat which accumulates in the roof space but there have been cases of people being kept awake by the constant drone of the motor and fan.

The large fans move a high volume of air but for most of the time they turn slowly so the velocity is low which means that they are not likely to be a nuisance in the garden. The real objection to mounting them on a patio is the icy blast which is clear proof that they have extracted a lot of heat from the air. The defrosting cycle is completely automatic so there should be no problems with them icing up. Aesthetically they have work to do because they just aren't that attractive and are surely destined to be hidden away inside green hutches. We have seen them hidden away in bushes but this cuts down on the air flow and often makes them difficult to service. They also need to be as close to the heat store as possible.

Gledhill who have partnered Mitsubishi have come up with a thermal store specifically for heat pumps. Even though by thermal store standards the unit isn't huge it still took three men to carry it upstairs to the airing cupboard and if it ever needs replacing it will no doubt take another 3 to get it out. If possible it is best to locate the thermal store on the ground floor near to the heat pump. A garage or utility room would be ideal. We would also suggest that Gledhill comes up with a better stand than the wooden pallet that they currently supply for the unit to sit on. Four jacking feet on two metal tracks, which could then orientate to span the joists, would be better.