As demand rises for ever more efficient heating and cooling of homes, this has seen a significant push towards efficient residential heat pumps. As a direct replacement for gas condensing boilers and air conditioning units, residential heat pumps can provide year-round comfort control by supplying heat in the winter and cooling in the summer. For newer buildings and specifically for net zero carbon buildings less than 150 m2 then typical heating power ratings are below 6 kW. Regardless of whether they are air-to-air or air-to-water systems, efficiency and carbon footprint can be further improved when powered by a photovoltaic (PV) installation.