# Sizing a Heat Pump

In one of my earlier blogs, I described to you how a heat pump works. Now I am going to tell you about how it looks from the installer’s side when putting in a correctly sized heat pump.

A heat pump, whether its ground source or air source must be sized correctly. If its too big, it will not work efficiently because it will produce more heat than required. If its too small, it will not provide sufficient heat for the home and you’ll feel chilly.

Let’s take a step back. To ‘size’ means to calculate the required power output from the heat pump. For a small home this might be 5kW and for larger homes, say, 14kW. This means that the heat pump will output 14kW of power when working at capacity. At other times, it will be lower as need decreases.

It is therefore really important to know what the energy needs of the home are. This requires very careful calculation. This requires the height, width and length of each room; the room’s situation i.e. number of internal/external walls, ground floor/first floor; the floor, ceiling and wall building materials; number of windows and their construction (double-glazed, argon filled).

Using this data, the room ‘u-value’ is worked out. This is basically the rate at which the room loses energy. In a stone walled room with a timber floor and no insulation, the u-value will be high. On a brick and breeze block construction packed with insulation, the u-value will be low.

This process is repeated until the whole house is accounted for. All of this is put together and the size of the heat pump worked out.

So you can see that for this kind of installation, even quoting for a job takes time and great care. As an installer, getting it wrong is a total nightmare and to be avoided at all costs. It has not happened yet, and you can be assured that BEC will maintain our high calculation and installation standards to ensure it never does.

For a very handy working example of a heat pump calculator, follow this link:

http://www.microgenerationcertification.org/installers/installers/mcs-heat-pump-software

Why not have a go using the data from your own property?