A successful heat pump installation begins with defining goals, gathering data, and calculating the heating and cooling needs of the house. The next step—zoning and equipment selection—is often the most challenging, in part because of the large number of choices. Will the house be served by a ducted air handler, one or more ductless heads, or some combination? If there are multiple indoor units, will they connect to a single outdoor unit? What types of indoor units will be used? Where will they be located, and how will they be sized?

In approaching these decisions, it’s good to know the full range of options. Most folks with a basic knowledge of heat pumps are already familiar with high-wall ductless heads and centrally ducted air handlers. But several other styles of indoor units are available. In this two-part series, I’ll give an overview of the main types, including their general characteristics, strengths, and shortcomings. Here, I’ll look at ductless options: high-wall units, low-wall (floor) units, and ceiling cassettes.

Ductless options

Ductless indoor units, as their name implies, are not connected to ductwork, grilles, or registers. They pull air directly from the space in which they’re installed and discharge heated or cooled air back into the space. In homes with no existing ducts, or with ducts in poor condition, ductless heads are often the most cost-effective and least invasive option.

Eliminating ducts also allows for quieter, lower-powered blower fans and avoids the efficiency losses that occur when ducts pass through unconditioned spaces like attics. On the downside, ductless units have limited filtration and dehumidification capabilities and are not easily integrated with fresh air systems.

While a ducted system can be designed to deliver appropriate volumes of heated and cooled air to every room, a ductless design…