Most heat pumps are classed as split systems. This means they have two units - generally one inside and one outside - that are connected with ducts. For example, an air to water heat pump is a split system as you’ll have a fan unit and heat exchanger outside and a water cylinder and secondary heat exchanger inside. The other type of heat pump system is known as a packaged packaged. A packaged heat pump is all in one unit, which is generally outside. The heated or cooled air is then transferred indoors through pipework. An air to air heat pump can be packaged or a split system.