ASHP: Ducted or ductless? Mini-splits?

Learn more about different types of heat pumps and HVAC designs and what will work best for your home or business.

When reading about air source heat pumps, you may have come across terms like “ductless mini-split” (or maybe you haven’t, but read on!). As with a lot of other things related to building energy use, jargon can be confusing. This article will define some of terms you may have come across and discuss the advantages of different types of air source heat pumps. The good news is that all types of heat pumps work in pretty much the same way, though there are some differences in heating and cooling delivery.

Mini-split

A mini-split heat pump system usually describes an “split” air source heat pump system that uses one outdoor unit to serve the heating and cooling output of one indoor unit (also referred to as “single head”). Homes using mini-split heat pumps that need more than one indoor unit (for example, one on each floor or one on each end of a the house) would need to have multiple outdoor units as well. Think about it like plumbing: one main pipe would bring water into your house for each shower head that needs it. In the same way, a mini-split has pipes of refrigerant that move heat in or out of your house, bringing the heating or cooling to your rooms through the indoor head. Unfortunately, the term “mini-split” is not always used in the same way: some people use the term mini-split to refer only to ductless systems (see below), while others use it to just refer to heat pump systems that are smaller in capacity. Even still, others use the term mini-split to describe systems with more than one indoor unit for each outdoor unit. If you’re confused, don’t worry--it’s confusing even to the experts who are trying to get these definitions sorted out. On this website, when we use the term “mini-split heat pump” we will be referring systems with to one outdoor unit for each indoor unit. We will refer to systems that use one outdoor unit to serve multiple indoor units as multi-head systems. In all cases, these multi-head units will be ductless (see below).

Ducted vs ductless systems

Ducts are used in heating, ventilation, and cooling to move air around a building—you may have seen them in attics and crawl spaces, bringing heating or air conditioning from a single source to different rooms in a building. A ductless heat pump system will allow you to providing heating and air conditioning to multiple rooms without having to install a duct system, either through using a ductless mini-split or through using a multi-head ductless heat pump. Instead, a ductless system uses indoor units (or “heads”) to provide heating and cooling to each room. [Insert Photos] There are many benefits to choosing a ductless system.

• Duct systems can often be leaky if done poorly, reducing heating and cooling effectiveness and costing you potential energy savings of up to 30%.
• Duct systems take up space somewhere—often in the attic or basement—that you could use for something else.
• Ductless systems can be more appropriately sized for your building’s heating and cooling needs. Heads can be placed in multiple rooms, giving you the means to easily control how warm or colds each room gets.

There are also some drawbacks to ductless systems.

• Some consider the heads of ductless systems to be aesthetically displeasing. Fortunately, there are less unsightly ways to install indoor units: heads can be mounted on the ceiling (see pictured ceiling cassette) or disguised above doors, shelves, or cabinets.
• Indoor units will make some noise—not anywhere close to a loud window A/C unit, but if you need an absolutely silent house, a minisplit ductless system might not be the best solution for you.

The best way to figure out if a ductless or ducted system is best for you is to sign up for a WePowr community and get in touch with the community’s installer, who will be more than happy to answer all of your questions and provide a free site visit.