What Is a Mini-Split?
By Kevin Purdy
Table of contents
Mini-splits vs. window or portable units
A mini-split, or ductless air conditioner, is an appliance that can both cool and heat a home. But unlike a traditional air conditioning or heating system, mini-splits offer “zone-control.”
While a traditional heating and cooling system can be turned on or off, each indoor unit of a mini-split can be set to a different temperature. And each indoor unit only requires a few smaller lines run to it, rather than large ducts.
In addition to having more control over the temperature throughout your home, mini-splits tend to be more efficient than traditional air conditioners. And when turned to heating mode, they are between 2-4 times more efficient than a furnace, baseboard or a boiler.
In this article we’ll explain how mini-splits work, look at their pros and cons, and answer frequently asked questions about these high-efficiency heating and cooling appliances.
How does a mini-split work?
In many ways, a mini-split functions much like a traditional air conditioning system. In cooling mode, it moves heat from inside your home to the outside air. The difference is where the cool air blows from.
In a central-air system, the cool air comes out of a single “air handler” (basically a big fan in your attic or basement), then blows that cool air throughout all the ducts of your home. A mini-split, by comparison, can blow cool air from up to 6 seperate air handlers, hence why they can offer zone-control.
There’s more to the process, involving expansion, compression, and evaporation. You can read about the whole process in our guide to how heat pumps work.
Types of mini-splits
Number of zones
When you install a mini-split, you have to choose how many zones you want throughout your home. You can install one indoor unit to cover just a single room or zone. Or you can install five or six indoor units and make your whole home a modular heating playground.
Installing a single zone is ideal if you’re adding cooling or heating to a room that ducts are having trouble reaching, a new home addition, or an exterior space, like a garage or workshop. You could even consider a DIY mini-split kit for these kinds of projects.
A multi-zone setup typically allows up to six indoor units to be connected to a single outdoor unit. Each indoor unit is connected to an outdoor unit by thin lines of refrigerant, power, and drainage.
Where can you mount a mini-split indoor unit?
Because of their thinner tubes and cable connections, the indoor units in a mini-split system can go more places than a traditional ducted vent.
The most typical indoor unit you’ll see is a wall-mounted unit. These are generally mounted about 6 inches from the ceiling in order to distribute cool air downwards, as the warmer air will rise.
Beyond wall-mounted, other indoor units can be:
- Floor-mounted, for homes where windows, ceilings, or other room design prevents easy wall-mounting
- Floor-standing, for walls with even less usable space
- Ceiling cassette, for a more subtle look and better downward air spread
- Ceiling suspended, for more airflow but more noise, too
Benefits of mini-splits
By cutting out ducts and letting each indoor unit do some of the cooling work, a mini-split system gives you more control over exactly how you want your home cooled, heated, and dehumidified. Let’s walk through each benefit.
Individual control of each indoor unit
The indoor units in a mini-split system can be controlled with a remote control, a smart thermostat, or sometimes a mobile app. Rather than setting a single temperature to cover the whole range of your house, a mini-split lets you fine-tune for things like:
- Family members who disagree about the right temperature
- Rooms only occasionally used, whether at certain times of day(bedrooms, offices) or in general (guest rooms, attics)
- New additions or rooms in a home that don’t have ducts
- Individual rooms and areas with specific heating or cooling challenges (sunrooms, basements)
- Keeping pets comfortable in one room while you’re at work
Ducts are responsible for 20-30% air loss in a typical home, according to Energy Star. The cooling or heating coming from a mini-split system is generated at each unit so these losses can be avoided..
Another inherent advantage of mini-splits is allowing rooms or zones to be kept at separate temperatures (or turned off entirely). If your bedroom is across the house from where a main thermostat would go, a mini-split system could provide serious savings while you sleep.
Two major appliances for the price of one
In addition to cooling your home, mini-splits can also heat your home, which means when you install them you can avoid paying for a furnace or baseboards.
In heating mode, mini-splits use the same kind of no-duct thermal energy transfer to heat your home. And like all heat pumps, they can do it up to four times more efficiently than any other heating system.
You can use a heat pump with a ducted system, but a mini-split system (which also uses heat pump technology) delivers this heat the most efficient way possible
Ducted HVAC systems typically have one filter installed in a central, indoor location. Cleaning out the ducts typically requires professional service, which can put homeowners off the job (ask us how we know).
By comparison, each indoor unit in a mini-split setup has its own air filter that can be replaced by the homeowner with nothing more than a stepladder.
Whenever you turn on an air conditioner, you are also turning on a dehumidifier. With a mini-split this is the case, too. But mini-splits have one major advantage over traditional air conditioning systems in this regard.
Imagine it’s a humid, but not entirely hot, day in October. You might not want to turn on your air conditioner. But, for both health and comfort reasons, you definitely don’t want to sit in a humid home. With a traditional air conditioning system you have two choices: Sit in humid misery, or turn the AC and bundle up.
If you have a mini-split, you can turn it on “reheat dehumidification mode,” which sounds more complex than it actually is. In this mode you can keep the temperature constant while removing humidity from the air.
Downsides of mini-splits
Potentially higher upfront costs
Putting all-new ducts for a central air system into a home, especially an older home, is expensive.
But setting up a new mini-split system isn’t cheap, either. Even a single-zone system can cost $2,000-$6,000. Multi-zone systems that cover an entire home generally cost between $8,000-$12,000, according to homeowners and contractors we’ve talked to.
Mini-splits often require electrical work, ranging from the simple (like running a 220V line to each indoor unit) to the complex (like upgrading your electrical panel). Some homeowners even have to upgrade their electrical service entirely from 100 amps to 200 amps.
Aesthetics of wall units
The typical mini-split configuration has each indoor unit hung on a wall. Wall units can be black or white. Many would consider them inoffensive. But some people won’t appreciate having anything hanging on their wall.
As noted above, there are alternatives to wall units, like floor-mounted, flush ceiling, and ceiling-suspended units. But both the units and the labor costs tend to go up when you go with these options.
Mini-splits vs. central A/C
The case for mini-splits
As we’ve covered above, mini-splits have a lot of advantages over traditional air conditioners. Those advantages include:
- More control over the temperature of individual rooms and spaces
- Higher efficiency and less energy loss through ducts
- The ability to heat your home up to 4 times more efficiently than a furnace or baseboard heater
- The ability to dehumidify your home without cooling it
- Cleaner air on average
The case for central AC
Mini-splits aren’t for everyone. Here are the main advantages of central air:
- Lower upfront cost if you want to cool your entire home
- Less electrical work required
- Less obtrusive aesthetic
Mini-splits vs. window or portable units
If your summers are mild and you typically only cool one or two rooms, you might be tempted to stick it out with window units. If you’ve ever installed and used a window A/C unit, you know their inherent drawbacks:
- They block light and views through the window
- They’re typically unattractive, viewed both inside and outside the home
- They take up an electrical outlet, and may require thick extension cables
- Improper installation can lead to some surprising drainage problems
- They’re heavy
- They’re loud
- They make your windows less secure
Portable units may provide more placement options than a window unit, but still require a window for heat exhaust, and create their own setup headaches.
And both kinds of temporary units are less energy efficient than a mini-split.
The case for window or portable AC units
Window and portable AC units can be thousands of dollars cheaper to install than a mini-split. So if you just need to cool a room for a short amount of time, they can make more sense.
And unlike a mini-split, window units and portable air conditioners can be moved from room to room.
Frequently asked questions
Do I need a mini-split for every room?
Not necessarily. A larger indoor unit can work for a “zone” of a home, not just a room. And if a room doesn’t need heating, cooling, or dehumidification, you can skip a mini-split in there.
That said, it’s more efficient to buy a properly-sized indoor unit for each room where you might want cooling, rather than buy larger units and hope they’ll cover multiple rooms.
Are mini-splits noisy?
A mini-split has two main components, an indoor unit and outdoor unit. Both will vary in their noise of operation, depending on the capacity of the unit and the temperatures they’re trying to reach.
Manufacturers’ ratings generally show decibel levels of indoor units between 20-49, and outdoor units 45-60. Those are comparable, according to noise charts, to between a whisper and a library indoors, and a “quiet suburb” outdoors.
Can I install them myself?
MRCOOL, Pioneer, and other brands sell DIY mini splits in single-zone and multi-zone configurations. You can walk into a big-box store and come home with most of the gear required to install mini-splits in your home. But should you?
Using an HVAC contractor provides many inherent advantages to a DIY installation. Good contractors know the equipment they’re licensed to install. They’re familiar with your region, your style of home, and, of course, the type of work that needs to be done. And most importantly, manufacturers offer up to 12 year warranties on equipment installed by licensed HVAC techs.
That all might well be worth the dollars you’d save in a DIY installation. But if you’re technical and up for the challenge, give it a try. We’re heard stories of people saving thousands by doing a DIY install.
A good first step is looking up the manual of the model you’re considering and read it thoroughly. A typical DIY mini-split job involves electrical work, wall mounting, knowing exactly what’s inside your walls and drilling holes through them.
What are the electrical requirements for a mini-split?
Most high-efficiency mini-split systems require 208-230-volt service. Some smaller units only call for 110-115 volts, and could therefore rely on typical household power. Your HVAC contractor should know what your system demands, and whether your home’s current panel and service can provide it. If you’re at all uncertain, seek out a qualified and licensed electrician.
Do mini-split units come in colors other than white?
If a white mini-split wall unit isn’t appealing, you can take some comfort in having at least one other option: black. You’ll have to do some hunting for black wall units, however. Beyond black and white, there are not a lot of color options, whether indoor or outdoor.
As noted above, if a white or black wall unit unacceptable in a room, there are options for ceiling or floor mounting.
How can I camouflage or cover up a mini-split?is
Beyond choosing a ceiling or floor-mounted mini-split unit, one manufacturer, and some DIY tricks, do offer a way of improving, if not hiding, the look of a wall unit.
LG’s Art Cool line provides a frame in which you can place any image you choose, with the heating or cooling coming out of the sides of the wall unit. You and your contractor can also try some creative placement: in bookcases, inside old-fashioned radiator covers, under stairwells, and more. Anything that doesn’t block access to the air, the filters, or the equipment for service, and doesn’t put them too close to electronics, is fair game.