Ductless "Mini-Split" Heat Pumps
Imagine an extremely efficient window unit... but without the window. That's essentially what a mini-split is. It uses refrigerant to transfer heat between indoors and outdoors, just like a regular heat pump. But, it circulates air without ductwork, only in the room in which it is located.
These units are available in both A/C only and also in heat pump models. The higher quality heat pump models use an "inverter" technology in their compressors, allowing them to deliver more btu's than most traditional heat pumps at a given outdoor temperature.
Multiple indoor units can be hooked up to a single outdoor unit, allowing each area to be individually controlled. This is an ideal retrofit solution when installing ductwork is either not possible or desired.
These units are quite common outside of the US and tend to be much more efficient than ducted systems because they directly cool and dehumidify the air of the room they are in, can be individually adjusted, and are not prone to duct losses.
