Centrally ducted ASHPs, also known as central ASHPs, consist of an outdoor unit with an integrated compressor, an indoor air handling unit, and refrigerant piping connecting the units. These systems tie in to a home's central ducting, which is used to distribute conditioned air. Centrally ducted ASHPs with single stage compressors are the lowest cost variant but they are also the least efficient. Units with two-stage or variable speed compressors are more costly but they are more efficient and better able to tune their output to the space heating and space cooling requirements.

Source: ACEEE Summer Study on Energy Efficiency in Buildings, 2008