This depends upon whether you choose horizontal ground loop or vertical borehole installation. Horizontal ground loops need the most space – typically at least three times your total floor area (including ground and upper floors). Vertical boreholes can be installed on a smaller plot, but there are restrictions as to how close these can be sited to buildings, so it is best to check with an expert before making a decision.
Don’t forget to account for space within your home for the GSHP, cylinder and buffer tank – most people choose to locate these in a separate plant room.