Heat Pumps

The traditional homes of Cheltenham are not ideal for heat pumps. Heat pumps deliver a slow, regular flow of heat rather than big bursts of heat. This means that they are best used in very energy efficient and air-tight homes that only need a background heat input. By contrast, many traditional homes in Cheltenham are relatively draughty and poorly insulated. Fitting a heat pump to this sort of property could result in your heating bills going up rather than down.

Heat pumps are electrical machines that pump heat from cold places into warm places. They are called heat pumps because the heat is being pushed against its natural direction of flow. Just as an ordinary pump moves water against gravity, from low level to high level, so a heat pump moves heat energy from a low temperature source to a higher temperature output.

A fridge is a heat pump: heat is taken out of a cold place (the interior cabinet), making it even colder, and released out of the back of the cabinet, making the room marginally warmer. Home heating systems that use heat pumps work in the same way. Heat energy is taken from a cool source, such as the ground or the outside air, and transferred to maintain the temperature of the hot water that is pumped round the pipes of the heating system.

Heat pumps are clever machines but they take a lot of electricity to do all that pumping. And although the heat in the ground is there for the taking, the electricity will cost you.

Ground Source Heat Pumps

A ground source heat pump that is well specified and well run will deliver 3-4 units of heat to a home for every unit of electricity it takes to run it (this is known as its co-efficient of performance or COP). But electricity is around three times as expensive as gas, so you will be lucky if the costs of running it are any lower than an efficient gas boiler (and it is much more expensive to install). Also, mains electricity is almost three times as carbon intensive as gas, so a heat pump powered by mains electricity is not saving much carbon (if any) compared to a gas boiler.

Ground source heat pumps are also only generally suitable to properties with quite a bit of outdoor space, as they are usually installed by digging long trenches in big gardens and laying pipes one metre down – so not generally urban Cheltenham. It is also possible to install a ground source heat pump using vertical boreholes but this is expensive and requires access for a drilling rig.

Air Source Heat Pumps

Air source heat pumps are usually more carbon intensive than gas because they only deliver 2-3 units of heat for every unit of electricity. Most heat pumps are installed in areas where mains gas is not available so the building is reliant on electricity for heating.

Because the intake of an air source heat pump looks like an air-conditioning unit, for aesthetic reasons you may also face problems getting permission to install an air source heat pump in a historic residential area, unless you can install it in an unobtrusive location, a hidden intake in a valley roof would be a good choice, for example.

If you have a watercourse near you (such as a river, lake or canal) a water source heat pump could be another option.

Thus, if you want to save money or carbon, you should generally only consider a heat pump if

a) you have done an extremely thorough job of insulating and draught-proofing your home to a high level.

b) you have enough garden for a ground source heat pump.

c) gas central heating is not an option

You may also need to resize your heating system, for example with larger radiators or under-floor heating, as heat pumps work best producing heat at a lower temperature than boilers.

Therefore, if you are interested in installing a heat pump, you should do your sums and get expert advice, in order to ensure that it will be a worthwhile investment. You should also spend some time with the installer and/or the manual in order to ensure that you are completely confident about how to operate the machine properly. Recent trials in Britain have revealed poor householder understanding of heat pump controls, resulting in sub-optimal performance.

A typical Air-Source heat pump.