When Ductless Minisplits Make Sense
Easy-install, high-efficiency HVAC is ideal for retrofits and well-insulated new homes
Although they account for only 5% of the heating and cooling systems in the United States, ductless minisplits have attracted the attention of a growing number of builders of high-performance houses. In this article, contributing writer Scott Gibson explains how this unique type of air-source heat pump works, how it differs from a conventional air-source heat pump, and in what conditions it performs at its best and its worst. A minisplit consists of an exterior condenser and one to eight interior heat exchangers. Instead of sending conditioned air through a system of ducts, a ductless minisplit sends refrigerant through small-diameter supply lines in the walls to each heat exchanger, where a fan blows air over an evaporator to either heat or cool the space. Not only is it easier to retrofit most houses with a ductless system than a ducted one, but minisplit distribution losses are generally much less than those of a standard air-source heat pump. Although minisplits perform better in cold weather than standard air-source heat pumps, in a leaky, under-insulated house, they may not be able to produce enough heat in very cold temperatures. This can require supplemental heating and/or be an incentive for the homeowner to tighten up the envelope. A sidebar written by senior editor Andy Engel explains how heat pumps work.