Many current-generation residential HVAC product providers sell their wares as a system. A typical air-to-air heat pump system is a good example. If it’s a ducted system, the air handler, refrigerant line set, outdoor condenser unit and even the thermostat are typically sold as a matched set of components. It’s a similar story for ductless heat pumps. A given condenser unit is rated to handle a specific number of specific indoor wall units. The DX line sets are all prescribed along with allowable lengths based on the refrigerant pre-charge in the condenser units. The controls are typically hand-held remotes.

This approach is nice in that it simplifies design and product selection. It also ensures compatibility between all the major components involved.