Heat pumps are best suited to well insulated, energy-efficient homes. Unlike boilers, they cannot produce a huge surge of energy to heat up a house quickly but prefer to chug away in the background, providing a regular output of heat to keep the building at a stable temperature. If you live in a house that cools quickly and is often unoccupied during the day, a heat pump will not be your best option.
Heat pumps become less efficient as the difference between their source and output temperatures increases. Consequently they are ideal for underfloor heating which operates at a lower temperature than radiators. To enable the heat pump to work efficiently, radiator systems may have to be upgraded with bigger radiators which emit more heat
The ground works for a heat pump can be substantial. Depending on the space available, you can either dig long trenches for the pipework in your garden, at about 2m deep, or put the pipes down a 75-100m borehole. Get a survey done first to ensure that the ground is suitable. The trench option is easier and cheaper but may seriously mess up your garden during installation.
Some heat pumps do not need ground works: air source heat pumps extract heat from the ambient external air or, in some models, from the exhaust of a mechanical ventilation system. Unlike the ground which stays at a stable temperature all year, the air gets very cold just when you want to extract the most heat from it, so the efficiency of air source heat pumps can be very poor. They should only be considered for small properties with very low energy demands.
It is also possible to draw heat from water such as a flowing river. This can be a good heat source because the extracted heat is rapidly replaced.