Air Source Electric Heat Pumps
This is the most common type of heat pump, and there are two basic kinds. The layout of your home will usually determine which one you'll want.
Packaged heat pumps
The packaged heat pump is a self-contained unit that allows the compressor and both heat exchangers to be located outside your home. The unit uses ductwork to heat and cool your entire home. Several types of packaged heat pumps, called packaged terminal, self-contained through-the-wall, or window heat pumps are used for single rooms and don't need ductwork.
Split-system heat pumps
The second type, called the split system heat pump, is the more common of the two air source choices. In this type the indoor air-handling unit and heat exchanger are separate from the compressor and the outdoor exchanger. This allows you more options on where you install it. Whole-house heating and cooling occurs via ductwork.
There are also two special kinds of special split-system heat pumps. The triple-function heat pump not only warms and cools your home, it also heats your water. By removing heat from the system's refrigerant and using it to heat water, it provides essentially free water heating during the summer and a much more efficient use of electricity for heating water in the winter.
The free-delivery split-system heat pump has one outdoor unit and one or more indoor units. It allows you to heat or cool individual areas in your home by circulating refrigerant to each indoor unit. Each area has its own thermostat. No ductwork is needed.
Efficiencies
The heating efficiency of an air source heat pump is measured as the Heating Seasonal Performance Factor (HSPF), and typically ranges from 7.7 to 8.1. Cooling efficiency for these heat pumps is indicated by the Seasonal Energy Efficiency Ratio (SEER), which typically falls between 13.0 and 16.0. The higher the number, the better the system.