Ductless minisplit heat pumps are widely used in Asia but so far have a relatively small share of the market in the U.S., accounting for only about 5% of installations for heating and cooling systems. Given a number of key advantages over conventional air-source heat pumps, that could change.

Both systems work on the same principles. The big difference is in how conditioned air is distributed. With a conventional air-source heat pump, an outdoor condenser/compressor supplies a central indoor evaporator/air handler with pressurized refrigerant. Conditioned air is blown through ducts to individual rooms.

In a ductless system, the outdoor unit supplies as many as eight individual indoor units with refrigerant through a small-diameter line. There are no ducts. Each indoor unit can be controlled separately, making it relatively simple to manage heating and cooling in different parts of the house.

One of the best known systems is the Mr. Slim manufactured by Mitsubishi, but ductless minisplits are made by a number of companies, including Fujitsu, LG, Frigidaire, Friedrich, Lennox and a number of others.

Ductless minisplits often are promoted primarily as an easy way of adding air conditioning to homes without ductwork.This is true, but they also can provide heat. They are an increasingly popular choice for high-efficiency houses with low heating loads.

Eliminating the need for ducts saves money, and a ductless system also is less disruptive during a renovation. In a ductless system, a 3-inch-diameter conduit provides enough room for the refrigerant piping, control wires and a drain for condensate. A simple system that includes an outdoor unit and a few indoor heads can be installed quickly, with little of the construction headaches associated with a conventional system.

Ducts also are inherently wasteful. The U.S. Department of Energy estimates that as much as 30% of…