Where it is not possible to drill in a ground probe or install a surface ground loop on the property, an air source heat pump may well be the answer. The only space requirement is an outside wall making them ideal for apartments and homes with limited outside space. With no need for ground works, installation costs are kept to a minimum. Air source heat pumps work by converting the energy of the outside air into heat, creating a comfortable temperature inside the house as well as supplying energy for the hot water system. As with all heat pumps, air source models are most efficient when supplying low temperature systems such as under-floor heating.