Green builders usually specify high-performance windows and above-code levels of insulation, while striving to reduce air leaks in their homes. As a result of these efforts, most green homes have relatively low heating and cooling loads.
Increasingly, these low-load buildings are being heated and cooled by ductless minisplits or ducted minisplits. Many of these air-source heat pumps have ratings in the 9,000 to 15,000 Btu/h range — an appropriate range for low-load houses. Because they are fueled by electricity, these systems are a good match for a home equipped with a roof-mounted photovoltaic system.
Of course, there are still plenty of builders who have their doubts about minisplits. Some wonder whether it’s really possible to heat and cool a house with just one or two ductless minisplits; others wonder whether every bedroom needs a separate heater or forced-air register. (GBA has published a quite a few articles on those topics; for links to these articles, see the “Related Articles” sidebar below.)
In this article, I won’t be addressing questions about cold bedrooms or providing advice on bedroom door operation. Instead, I’ll assume that readers know how many ductless or ducted units they want to install — but just want some guidance on equipment selection.
To keep things simple, this article will focus on just two manufacturers: Mitsubishi and Fujitsu. These two brands have captured a strong percentage of the U.S. market for minisplits, and both companies manufacture equipment that works well in cold climates.
Start with a load calculation
When designing a heating and cooling system, the first step is always to perform a heating and cooling load calculation — ideally one using the Manual J method.
Be careful: many HVAC contractors don’t know how to perform these calculations. The vast majority of HVAC contractors use rules of thumb that…