For small houses, 1-2 borehole heat exchangers or a horizontal collector. A larger house may need more, but they are space close together. The installation is not visible from outside, the heat pumps (incl. buffer tanks and/or DHW tank, where appropriate) do not need much space, and a fuel oil tank or connection to the gas grid is not required.
A larger residential house in Virginia, using the latest ClimateMaster equipment.