The amount of space available outside your home will likely play a role in your choosing between air source and ground source heat pumps.
On one hand, ground source heat pumps require a large portion of your garden to be dug up, however the efficiency of the heat pump will more than make up for it in the long run. On the other hand, air source systems require very little room comparatively because they absorb heat from the air. It does lose out on efficiency to the ground source system, but if you’re short on outdoor space, air source heat pumps are the cheapest option and quick to install.
Air source heat pump
The external unit in domestic air source heat pumps is no larger than a washing machine, and can be located anywhere where there’s a decent flow of fresh air (or ambient air flow) and a bit of breathing room. To keep installation costs down, the heat pump can be connected to the buffer tank inside via an existing flue (a vent or outlet for steam on the outside wall of your home), but if you’re worried about aesthetics, the box can also be wall mounted to the back of the garage or hidden away in the garden.
In terms of power output, there are a few options to choose from depending on how much heat you require, but 5kW, 8kW and 12kW systems should cover the demands of most households providing they have basic levels of insulation. As a guide, it generally takes 1 Kilowatt of heat to warm every 10m² of a house (subject to insulation and heat loss).
Ground Source Heat Pumps
Ground source systems aren’t as easy to install as their air source counterparts, nor are they as compact. The pipework for ground source heat pumps can be laid in one of two ways – either horizontally in trenches or vertically in boreholes. For an idea of how much space you’ll need, the Centre for Alternative Technology suggests that a standard ground source heat pump needs somewhere between 50 and 80 metres of pipe per kilowatt, or just 10 meters of ‘slinky’ coiled pipe. Our rule of thumb is that standard trench loop systems need roughly twice the total floor area of your home from every storey.
So long as the ground is suitably porous to conduct heat, the area is systematically divided and dug into long trenches, before the piping is laid roughly 1.2 metres below ground. As this will cause quite a lot of destruction in your garden, it’s a good idea to coincide the heat pump installation with some major garden remodeling. Boreholes require less horizontal space, but whether they are suitable depends on the geographical location of your home and the drilling procedure can be rather costly.
The size of the buffer tank and hot water cylinder will depend on how large your home is, but generally speaking all internal components should fit into a small utility room.