Heat pump unit with the refrigeration cycle contained within one unit 'monobloc' which is then connected by piping to the heat distribution system. No refrigerant flows outside of the monobloc casing – just water, making installation possible by a plumber.

Heat pump unit with the entire refrigeration cycle being 'split' between separate outdoor and indoor units – which are connected using piping filled with refrigerant. Installation requires a refrigerant engineer.

Heat is extracted from ambient external air and transferred to another medium. The heat available reduces as the temperature of the air reduces reducing both performance duty and efficiency: See also [..]