Ductless Mini-Split Heat Pumps 101: How They Work and Whether You Need One

Katy Willis
Written by Katy Willis
Updated January 27, 2022
woman in kitchen with her family adjusting temperature
Photo: Carlos G. Lopez/ Moment/ Getty Images

Highlights

  • Ductless mini-split heat pumps are an easy HVAC solution that doesn’t require ductwork.

  • These split systems can help reduce energy consumption and costs.

  • Ductless heat pumps can heat and cool your home.

  • Can run up to four interior units off of a single exterior unit, perfect for controlling temps in a home extension.

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Ductless mini-split heat pumps let you heat and cool your whole home or a single room without installing expensive ductwork. While ductless systems may not be the right choice for everyone, they have advantages—especially with homeowners who want to regulate temperatures in a new home addition. 

For example, maybe you’re contemplating air-conditioning the garage but don’t want to tear open the ceilings and drywall to do it. A ductless mini-split heat pump might just be the solution you’re looking for. 

What Is a Ductless Mini-Split Heat Pump?

Ductless mini-split heat pump systems are HVAC units that don't require ducts, making them extremely popular, practical, and cost-effective in certain homes. Similarly, if you're trying to minimize the cost of your home addition, you can save money by not having ductwork installed by choosing a mini-split system instead. 

While most are commonly found in smaller homes, annexes, or additions, ductless mini-splits can also work in larger homes where having more control over your heating or cooling could be beneficial. Enter HVAC zones. HVAC zones are a smart way to reduce energy costs because you only heat or cool the rooms you're actively using instead of the whole house (more on this below).

How Do Mini-Split Heat Pumps Work?

Ductless mini-split heat pump systems have two units. The indoor air handling unit is suspended from the ceiling or located at the top of a wall. This indoor component pumps the heated or cooled air into the room. It is connected to the second component—the outdoor compressor—via a power cable, a refrigerant line, suction tubing, and a condensate drain line.  

The outdoor unit creates air and then passes it to the indoor units via a forced-air system. It’s also where the compression and decompression of the refrigerant happens. You can have up to four indoor units for each external unit, and you can have as many exterior units as you need. 

While installing a ductless mini-split heat pump system is easier and less invasive than installing a new air conditioning system, there's still significant room for error. Therefore, you'll need to hire a local HVAC pro to take care of the installation for you.

Pros and Cons of Ductless Mini-Split Heat Pumps

While there are countless benefits of mini-split heat pumps, they are not for everybody.

Pros

With no ductwork required, mini-split heat pumps are fast and easy to install (though it will require professional work). These units provide both heat and cooling, so you’ll only need one exterior unit for all seasons. With a hand-held remote control, you can control the temperature in your room without leaving your couch.

Because you can condition the air in just one or two rooms instead of the whole house, mini-splits can reduce your energy consumption and costs by up to 30%. No ductwork means no wasted energy.  

Cons

Mini-splits create ductless zones, which means they may not be suitable in very cold or extremely hot climates. That's largely due to this type of system's inconsistent temperature control and airflow.  Though some modern ductless heat pumps can handle cold temperatures, they will vary based on your chosen system. Some homeowners in particularly frigid climates find they need a fuel backup.

Aesthetically, mini-split heat pumps aren’t so great. The units take up visual space on your wall or ceiling, which can clash with your decor. 

It’s also worth noting that ductless mini-split heat pumps don't dehumidify the air when on a heating cycle. If high humidity levels are a problem in your area, you'll need to add a dehumidifier to the system for the winter months.

Creating HVAC Zones With Mini-Splits: An Added Benefit

ac ductless mini split system
Photo: C5Media/ Adobe Stock

One popular method for most effectively using ductless mini-split heat pumps is to create zones for customizable comfort (i.e. only heating or cooling the rooms you're actively using at any given time, instead of the whole house). A single room that contains a mini-split indoor unit is considered a zone. In a whole-home mini-split system, each floor becomes an independent zone, with each zone running off a single exterior unit with up to four interior units connected to each.

In these multi-zone setups, homeowners often forgo placing interior units in hallways and utility spaces to limit the number of external and internal units required. 

However, the only way to keep a single room at a constant temperature is to activate the interior unit for that room and shut the door. You can warm unconditioned spaces such as hallways by turning on the closest interior unit and leaving the connecting door open.

Can a Mini-Split Heat Pump Both Heat and Cool?

In short, yes, a ductless mini-split heat pump can provide both heating and cooling. The exterior unit houses the components that result in the heat exchange process. The refrigerant passes through a series of coils and undergoes evaporation and condensation, propelled by the compressor pump. 

When switched to the heating cycle, the refrigerant absorbs heat during the evaporation and condensation process. Then, that heat is transferred to the air and forced into the room. The process reverses during the cooling cycle; heat is removed from the air and dispersed outside while cool air is pumped inside.

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