Single-zone units have one outdoor unit and one indoor unit. These systems are the most efficient units for heating your home or business and often provide the best return on investment.
The indoor unit uses a fan and a heat exchanger – much like the radiator in your car – to distribute heat or to provide cooling in the area served by the unit. These units are rated to outdoor temperatures of -5F and will work to -15F. Since it is more difficult to extract heat from the outdoor air as it gets colder, the output of these units decreases as it gets colder outside. As a result, auxiliary heat – such as a furnace, boiler, or electric heat – is often necessary to maintain comfort as the outdoor temperatures drop.
Multi-zone systems have one outdoor unit and multiple indoor units. While these systems are less efficient than single-zone units, they provide the benefit of heating and cooling various rooms in the house without requiring multiple outdoor units. Like single-zone units, the performance of these units decreases as the outdoor temperatures falls.
Multi-zone heat pumps may make sense if a home is heavily partitioned or if multiple air conditioners can be replaced by the heat pump.