Mini Split- Ductless Heating & Air Conditioning: What It Is + Why You Need One

Cooling and heating a house is a costly endeavor. But proper temperature control will provide greater levels of comfort and can contribute to your home’s overall health. (If you can’t imagine how temperature could affect a building’s integrity, think of frozen pipes and rotting support beams.) 

If you’re looking for an energy-efficient way to heat and cool your house, you might want to consider using a mini split. 

What Is a Mini-Split?

A mini-split uses a split system to heat and cool a house. 

Let’s break down the name. “Mini” refers to the (typically) smaller size of these units compared to traditional HVAC systems. 

“Split” indicates that the system relies on both an indoor and outdoor unit. (A traditional “packaged” HVAC system combines cooling and heating in a single outdoor unit.)

Mini-splits are different from conventional HVAC systems, although they perform many of the same functions. The main difference is that most mini-splits do not operate using air ducts. Mini-splits provide flexible heating and cooling for individual rooms rather than conditioning your entire home. 

Types of Mini-Splits

First, let’s clarify some potentially confusing terminology: mini-splits, one-to-ones, and multi-splits.

Mini-splits are heating and cooling systems where one outdoor unit connects to one indoor unit. Some people refer to this connection as a one-to-one.

But you can also have an outdoor unit connected to multiple indoor units. Some people distinguish this system by calling it a multi-split. 

(For the sake of simplicity, this article refers to all of these connections as mini-splits.) 

The most common mini-split indoor unit hangs on walls at eye level or higher. But you can also find units that rest on the floor or function through ceiling cassettes.

Most minisplits operate without relying on ducts. However, you can find instances of mini-splits installed using multi-position ducts. (Some people use the term “mini-split” exclusively for ductless units.) 

Usually, mini-splits use an inverter-driven variable-capacity compressor. In some rare cases, mini-splits will run with a fixed-capacity compressor, essentially a smaller version of a conventional heat pump. 

Where Will You Find Them?

Minisplit systems are hyper-efficient solutions for individual rooms, particularly areas that are difficult or impossible to reach with conventional air ducts. 

Here are some key locations that might benefit from mini-split cooling and heating: 

  • Master Bedrooms
  • Guest Rooms
  • Finished Basements
  • Attics
  • Garages 

The master bedroom is typically the farthest room from noising heating and cooling systems. But if you’re the kind of person who can only sleep when the temperature is just right, consider adding a mini-split to focus on that room. 

On the other hand, less frequently used spaces such as guest rooms, finished basements, and attics can benefit from mini-splits. Your house’s initial ductwork might not extend to these spaces, but you’ll still want to keep them comfortable when they are in use. 

If you’re in the process of planning a finished attic, check out this article on attic insulation. Proper insulation and a mini split will make the space much more comfortable.

Safety hazards prohibit the installation of ductwork in garages. But if you use your garage as an at-home gym or DIY space, you might want to use a ductless mini-split to control the temperature. 

Some buildings might lack a basement or space to install an air conditioner and furnace. Minspits can also provide a heating and cooling solution for these buildings. 

Are you worried about a mini split ruining home decor? You can hide a mini split. Here are four methods to use for the perfect hidden ductless mini split.

How They Work

man working on ductless mini split air conditioner

Mini-splits run off the electrical power and function like a heat pump. 

Like a heat pump, mini-splits collect heat from the outside and then bring that heat into your house rather than generating heat. 

But how do mini-splits gather heat from the outside in the middle of winter? Believe it or not, even winter air contains heat to absorb. 

Heat flow occurs when there is a temperature difference. Say you want to extract heat from air with a temperature of 22° F. You will need to put that air in contact with air colder than 22° F. This is why your mini-split contains refrigerant. 

During the refrigeration cycle, the refrigerant’s temperature drops as pressure pushes it through the expansion valve. This process means that the outdoor air is the warmer substance when it contacts the mini-split’s outdoor coil. 

To paraphrase the Second Law of Thermodynamics, heat moves from warmer objects to cooler objects. So the heat extracted from the cold air goes into the refrigerant. Then the mini-split transfers that warm air into your home.

The cooling function operates on the same principles, just the other way. 

A mini-split system will have a certain amount of indoor units (up to eight) that each function separately. You will also hear people refer to these units as heads. Multiple heads allow you to use only as much as you need. 

Larger HVAC systems disperse a uniform temperature throughout the house. Minisplit heads let you adjust the temperature per individual room. 

Pros & Cons

The buzz about mini-splits these days is that they’re more energy-efficient. But does a mini-split actually have a smaller carbon footprint than other heating systems? And what if energy efficiency isn’t your only concern?

Consider the following pros and cons when thinking about mini-splits. 

Pros

  • Energy Efficiency. Mini-splits use inverter technology to convert incoming high-voltage electricity into DC voltage. This technology allows your mini-split to do more work while using less energy. Thanks to a variable-speed compressor, mini-splits operate more like a dimmer on a light switch, unlike standard HVAC units that often turn on and off – saving precious energy.
  • Flexible Installation. Ductless mini-splits eliminate the need for bulky ducts that can be difficult to install in some locations. Using multiple mini-split units to heat and cool your house means you won’t lose total conditioning if one system goes down.  
  • Humidity Removal. Mini-splits include an evaporator coil. This coil collects condensation on the unit. It then drains that moisture outside your home.  
  • Air Filtration. Filters catch particulates. Plus, you can remove and clean these filters. 
  • Temperature Control. Mini-splits allow you to zone your heating and cooling. This feature means that families can adjust bedroom temperature to meet their individual preferences. Mini-splits also include temperature-gauging room sensors. This sensor helps maintain temperature consistency.

Cons

  • Single Room Coverage. In most cases, a mini-split head will heat and cool isolated spaces rather than an entire house. 
  • Cost Variance. Like when pricing traditional heating and cooling systems, the total cost for installing mini-split units can vary widely. The main determining factor is the type and number of heads you use for your system. Per zone, a single-head unit will be about $5,000 to $8,000. You’ll likely pay upwards of $11,000 if your system contains more than two zones.  
  • Maintenance. Minisplits require regular servicing. (Keep in mind that a traditional HVAC system will also need regular maintenance.) 
  • Less Advanced Air Filtration. Although mini-split filters are easy to clean, they are not as advanced as whole-home air filters. However, you can purchase additional carbon filters or small air purifiers to improve this function. 
dirty mini split air filter on air conditioner head

So what’s the verdict? Minisplit systems will likely become the standard for future high-performance homes. Although they perform best in airtight homes that are very well insulated, mini-splits will also effectively heat and cool less efficient homes. 

For optimal efficiency, use a one-to-one configuration and follow the steps in the next section. 

Tips for Mini Split Success

The earliest mini-split models gave these systems a bad reputation for poor performance. However, contemporary models do provide efficient heating and cooling. These days, temperature failures associated with mini-splits are usually the result of improper use or installation. 

Follow these tips to maximize the performance of your mini-spit: 

  1. If you live in a two-story home, you’ll probably need at least two mini-splits. Experts estimate that a single mini-split head will cover just over 1,000 square feet. 
  1. Heat smarter, not harder. Heat rises, so locate your heating unit on the first floor. Ideally, you’ll install the units low on the wall. Some units are available for floor-mounting, which will also help with heating. 
  1. You will need an upstairs unit to keep your second-floor cool. A downstairs mini-split will likely be able to heat the entire house, but it will only cool the floor where you install it. 
  1. Relatedly, avoid the temptation to oversize smaller zones. If you’re retrofitting in a space with an existing heating system, install a smaller heat pump to maximize efficiency. 
  1. Avoid multi-zone heating systems when possible. They aren’t as efficient, they don’t turn down very much, and they’ll be much more expensive.
  1. Minimize air leakage and achieve above-code insulation levels. Whether you are building a new home or upgrading an older house, an excellent thermal envelope is crucial to your mini-split success. This airtightness is simpler to achieve in new constructions than in a renovation.
  1. Add wall-mounted controls. This thermostat will identify the temperature in the room rather than the return-air stream, reducing air cycling.
  1. Buy monitoring equipment. This equipment allows you to track input. But be aware that adding monitoring equipment will increase your total installation costs by $300 to $1500.
  1. Take extra precautions in cold climates. If you live in an area where snow is likely, make sure a roof covers the outdoor component of your mini-split unit. (Make sure the roofing doesn’t restrict airflow.) 
  1. Don’t worry too much about cold-weather performance in Climate Zone 5 and warmer. Reviews consistently note that mini-splits the ductless mini-splits from manufacturers Fujitsu and Mitsubishi perform at outdoor temperatures lower than what the units are rated for.
  1. Large windows reduce temperature performance. If you’re building your home, consider installing smaller windows rather than oversized windows. Smaller windows reduce heat loss, allowing for more consistent heating during the winter. Conversely, smaller windows will reduce heat gain on hot, sunny days. (This is particularly true for east or west-facing windows.) 
  1. Keep doors open during daytime hours. Open doors will allow heat to travel more easily from the room where the mini-split is located to other rooms. 
  1. Beware of bonus rooms. If you have a spare room in an attic or above your garage, you will likely struggle to heat or cool this space unless you place the mini-split unit within the room. This decreased efficiency results from the room’s 5-6 surfaces that face outdoor temperatures. 
  1. Run your ductless mini-split every hour of the day. It might sound counterintuitive, but running your mini-split 24 hours a day will be more energy-efficient than turning it on and off. The design of mini-splits allows them to modulate. Turning the mini-split on and off will create higher energy bills and less even temperature. 

Follow these tips whether you’re trying to stay cool or keep warm. Either way, a mini-split could make your home more comfortable and energy-efficient.