Ductless mini splits: Everything you need to know

Mini split, ductless air conditioner, ductless heat pump—whatever you call this kind of HVAC tech, it’s a super-efficient, all-electric way to heat and cool your home, new or old, one room or every room, with no ducts or radiators required. 

Millions of mini splits have already been installed around the U.S., and with big new incentives to get people to switch to clean-energy heating systems, there will be millions more to come.

At EnergySage, we’ve helped hundreds of people get ductless heat pumps installed in their homes. Here’s what we’ve learned from real homeowners, vetted installers, and experts around the ductless HVAC industry.

For starters: When we say mini splits, we’re talking about ductless heat pumps. There’s actually no universally accepted definition for mini split, but this one seems to be the most common in the parts of the U.S. where they’re most common (mainly the Northeast). 

Ductless cooling has been popular for quite a while. And heat pumps (in their ducted form) have been perfectly ordinary in the South since the 1980s. By the early 2010s, high-efficiency ductless heat pumps started to gain a foothold in Northern New England, where oil-fired boilers were the norm in home heating. 

It turned out that this new generation of cold-climate, variable speed ductless heat pumps that worked well in parts of Asia also worked just fine in one of the coldest parts of America. They even saved some people a lot of money on their heating bills, and gave them built-in AC for the first time—all while saving loads of energy and carbon emissions compared to traditional heating equipment.

They’ve been getting more and more popular each year. Here’s why so many people love them:

Easy to retrofit into homes with no ducts

In homes with no existing ductwork, ductless mini-splits are usually the easiest way to add a permanent cooling system. This is most popular reason that people buy mini splits.

Some ductless pros have even told us that many if not most of their clients didn’t really care about the whole clean-energy heating angle at the beginning of the project—it just turned out to be a nice bonus.

If you do care about heating your home with cleaner energy but don’t have ductwork for a ducted heat pump, ductless mini-splits are still the go-to option.

Mini-splits are also a super-practical way to add heating and cooling to a shed, bonus room, or any other small space without an existing HVAC system. 

All told, they’re a big improvement over the noise and hassle of room ACs, and the safety risks and poor efficiency of space heaters.

There are some good arguments in favor of adding ductwork, or for connecting an air-to-water heat pump to your existing radiators. But mini splits are hard to beat on costs, convenience, and comfort.

Highly customizable

Every mini-split is made up of an outdoor unit, often called a condenser or compressor, and one or more indoor units, usually called heads. With some big mini-split brands, there are dozens and dozens of possible combinations of these systems.

You can get a mini-split that serves one room, or install an elaborate system that covers every room in the house. Each head is an independent heating or cooling zone, so you can set different temperatures in different rooms, or just turn off certain heads altogether while leaving the others running. 

While the heads usually mount high on a wall, they also come in variants that mount inside a ceiling, or low on a wall, or even in a very short run of ductwork. “Each has its pros and cons around aesthetics, installation dynamics, and price,” says Josh Lake, co-founder of Elephant Energy (a vetted installer on the EnergySage Marketplace). “Ceiling cassettes are the most requested.” 

Some brands put a little more effort into making their heads good-looking. LG even sells one that doubles as a picture frame.

Excellent energy efficiency

Like any heat pump, mini splits use a trick of physics to cut the total energy use by about two-thirds on average, compared to a traditional fossil fuel furnace or a “regular” electric resistance heater. (In cooling mode, it’s no different from a typical air conditioner.) 

This doesn’t mean you’ll always save money compared to gas heating, but you might—and you’ll almost certainly cut your carbon footprint. 

Mini-splits aren’t always the absolute highest-efficiency HVAC option. Ground source or geothermal heat pumps are more efficient than mini splits, but also much more expensive and difficult to install. Air-to-water heat pumps tend to save energy, too, but it’s hard to find installers for them in the U.S., and they don’t really do cooling. 

There’s also some evidence that as you add more heads to a single outdoor unit, a mini split’s efficiency can drop. But skilled contractors know how to design around the biggest pitfalls. And unless there’s a serious problem with the installation, they’ll still save loads of energy compared to any traditional heating system and most air conditioners.

Superior comfort

Since mini-splits (and other high-performance heat pumps) can adjust their power output, they can actually be much more comfortable than traditional HVAC. This is true all year, even in really cold weather.

It’s true that basic, old-school heat pumps don’t really work in winter weather. But modern, high-performance cold-climate heat pumps absolutely, unambiguously do. (You can still keep a backup system, if you want.) Several affordable models are rated to work flawlessly well below zero Fahrenheit. The chilly state of Maine is adopting heat pumps faster than anywhere else in the U.S. 

Extreme weather aside, the variable-speed design in modern mini splits also keeps you comfier in mild weather. In both heating and cooling modes, they’re built to hold a steady, consistent temperature (and humidity), rather than switching on and off constantly between full blasts, like traditional HVAC.

Most of the major air conditioner brands we see in North America sell mini-splits, but often don't actually manufacture them.

Then there are the true mini-split specialists, whose equipment you rarely see unless it's mini-split heat pump. The biggest names in the US are Mitsubishi, Fujitsu, Daikin, LG, Midea, and Gree.

Midea and Gree in particular are widely believed to be the original manufacturers of most of the mini splits sold under most other brands, including many of the biggest names in North American HVAC.

Based on quotes uploaded to the EnergySage Marketplace, the median cost of a ductless mini-split system in 2023 was $16,965 after incentives. But the range was enormous. 

Some small single-zone projects actually had zero out-of-pocket costs, while a few sprawling 8+ zone setups cost more than $65,000, even after rebates. That said, the majority of projects cost between $5,908 and $37,488. Multi-zone installations typically averaged out to about $4,000 to $6,000 per zone, a figure that held steady even as the numbers rose.

Surprised by the price of a whole-house ductless system? The thing to keep in mind is that you’re not just installing a new heating and cooling unit. You’re also adding the infrastructure to deliver the heating and cooling, like ductwork or radiators would handle in a traditional setup. So it might help to think of the project more like a small renovation, rather than a new appliance.

And remember: Mini-splits are so energy efficient that you could save a lot of money on your energy bills.

You can read much more in our full guide to mini-split costs.

Mini-split technology is rock-solid. It’s just a matter of getting a good installation, which means finding a good installer. 

Plenty of companies can do mini-splits, but it doesn’t mean they do them particularly well. Even HVAC pros with decades of experience in ducted or radiator-based HVAC might not get great results with ductless systems.

On the flipside, plenty of industry newcomers do excellent work with mini-splits—often aided by new quality-control software that takes a lot of guesswork and human error out of the system design.

All the pros on the EnergySage Marketplace are vetted heat pump experts, but if you need to look elsewhere for a good installer, we’ve got some tips on how to find them.

As far as the equipment itself, you’ll need a mini-split system that’s a good fit for your home and local climate. Again, a decent contractor should know what to pick. But if you want to double-check their work, read up on heat pump sizing, and how to choose a system that can keep up with the weather. (All ductless heat pumps currently on the market are inverter-driven models, which means superior comfort and energy savings.)

Multi-zone mini splits: Special challenges and how to handle them

Single-zone mini-splits are relatively simple systems, where the indoor and outdoor units are matched pairs that can operate together flawlessly.

But multi-zone ductless systems often have to make some compromises—usually in terms of energy efficiency, but it could also affect your comfort. 

An ideal multi-zone setup is one where a) the outdoor unit is sized correctly for the entire building, b) each indoor unit is sized correctly for the individual room or zone that it serves, and c) the capacity of all the indoor units adds up to exactly the same amount as the outdoor unit.

In the real world, that’s awfully hard to pull off, because the heat pump equipment only comes in so many sizes. 

Realistically, it’s A-OK if a ductless system isn’t a perfect fit for your house. There’s always some wiggle room, even if it means the system isn’t quite as efficient as you might hope. You just don’t want to see a massively oversized setup, because it’s going to be even less efficient, and pretty uncomfortable. 

(Unfortunately, these designs aren’t rare—but if you sign up for the EnergySage Marketplace, our Energy Advisors can help you spot the clunkers, and steer you toward setups that make more sense for your home.)

Skilled designers can find the right workarounds for your home. Here’s what they’ll look for.

• How is it going to be used? Despite the promise of room-by-room control, multi-zone mini splits tend to work better if all the zones are running simultaneously. But not everyone wants to use their mini-splits that way, and in that case the designer can help figure out a workaround

• Room sizes and airflow: You need to match the outdoor unit’s capacity to the house, and the indoor unit’s capacity to the room it’s serving—as closely as possible. This can be a little challenging: A small bedroom might only need 2,800 Btu of cooling, but the smallest indoor heads are 5,000 Btu. (It might even be better to rig up a short run of ductwork, and install one small compact ducted indoor unit to serve multiple tiny rooms.) Other rooms are so big that it can be hard to “throw” the conditioned air far enough that it mixes evenly. We’ve seen indoor heads installed in such a way that the warm or cool air gets trapped in one corner of a room, causing the unit to short-cycle—you’ve got to find a way to avoid that. Some rooms don’t have a good spot for a typical high-wall head, so you need to consider a different style. There’s almost always a solution, but the designer might have to spend some time thinking it through.

• Turndown ratio: The secret to the best performance here is having a low minimum capacity, relative to the maximum output—aka turndown ratio. "A big turndown is incredibly important for mini-splits," says Peter Freedman, an HVAC designer from Massachusetts with about a decade of mini-split experience. The outdoor unit dictates the system’s power output, so each individual indoor head can only turn down so low. And that might not be the ideal level for comfort and energy efficiency. The wider the gap between the lowest and highest capacities, the more leeway the system has to work well across more indoor units. Some popular systems turn down to about one-third of their maximum capacity, while others have a wider range down to about one-fourth of the max—enough to be a difference-maker.

• How many outdoor units? Depending on the brand, you can hook up anywhere from five to eight indoor units to a single outdoor unit—often enough to cover every part of a typical single-family house. On the EnergySage Marketplace, we often see those kinds of houses getting quoted for two outdoor units, with two or three indoor heads attached to each. There are pros and cons to either approach: Single ODU setups take up less space on your property and your electrical panel, and can cost a little less. But running all the refrigerant lines from a single outdoor location can present some challenges. Multi-ODU setups can be more energy efficient, and can avoid the challenges of those long refrigerant runs. But they take up more space, and we’ve seen several cases where they’re badly oversized.

Most installations take anywhere from 1 to 5 days, depending on how much equipment needs to get installed and how many installers are on site. Single-zone ductless systems go in quickly, while multi-zone setups can take much longer because of all the extra labor involved.

You can watch a whole-house ductless installation in the video above, and we also go into greater detail in this article. But in a nutshell:

1. Typically, the indoor units go in first. When it’s possible, contractors prefer to mount the heads near exterior walls, but it’s not a strict requirement.

2. Then come the outdoor units. It can be a bit of an art finding the right spot (or spots), especially on smaller properties.

3. After that, it’s time to connect the refrigerant lines to the indoor and outdoor units, as well as set up the electrical wiring and condensation drain lines.

4. Finally, it’s time to commission the system by releasing the refrigerant into the system, and adjusting the indoor heads for comfort.

What about DIY ductless?

A typical (professional) heat pump installation requires a handful of expensive specialty tools. Even if you’re willing to watch hours and hours of YouTube to figure out the process, the upfront cost just to try to install the system can be daunting.

However, a few mini-split brands sell do-it-yourself installation kits. The actual heat pumps and air handlers are identical to the equipment sold by bigger-name brands, actually. The main difference is in the refrigerant line, which is designed to be quick-connected without special tools.

Even with the quick-connect lines, a DIY installation is still pretty tricky and not a project to be taken lightly. 

You’ll need to be able to make sure all the components are installed level, and all the lines are at appropriate angles. It also means drilling at least one 3- or 4-inch hole through the side of your house, and pulling electrical wires. You’ll still need to hire an electrician, too, to set up the circuit and all the necessary safety features. It’s a lot of attention to detail. Multi-zone ductless systems or ducted setups can be even more challenging, especially if you hope to achieve decent energy efficiency.

Bigger picture, the quick-connect line sets could also be more prone to leaks than the flared or brazed connections that HVAC setups traditionally rely on. That means gradually diminishing performance and extra maintenance in the future—plus a big impact on the environment. Most HVAC pros won’t want to get anywhere near any mess that you’ve created on your own, either.

Mini-splits are super comfortable, highly efficient, and easy to retrofit into old homes at a cost that’s not too outlandish. Of course, they’re not without a handful of downsides. Here’s here ductless heat pumps can struggle:

Mediocre air quality and filtration

Ductless heads do have filters, but they’re just mesh screens meant to protect the system from getting jammed—not media filters that meaningfully clean the air. Evidence keeps piling up that clean air is a really good thing, but ductless heat pumps can’t help. (Ducted HVAC has a huge advantage here, in that it’s usually incredibly easy to equip those systems with an excellent filter.)

This isn’t because mini-split manufacturers are being cheap: It’s actually a major physics challenge to put a decent filter into a system that’s as quiet and compact as a ductless head. 

Apart from a missed opportunity to clean the air inside your home, ductless heat pumps could actually make your air quality worse if they aren’t maintained. When dust does sneak past the mesh filter, it can mix with moisture that has condensed on the coils or fan blades. That dark, damp, dirty environment is perfect for mold. This isn’t speculation; it’s a noted and growing problem. 

It’s possible to deep-clean the ductless heads after they get moldy, but it’s a tedious task given the compact design, and all-plastic construction. (To be clear, central ducted air conditioner coils can also grow mold, but they’re much easier to clean.)

A few manufacturers have launched or plan to launch new designs to prevent mold growth. And in the meantime, it’s a good idea to run another air cleaner in your home—even something as simple as an HVAC filter taped to a box fan can make a big difference.

Milder-feeling heat

Traditional heating equipment runs hot—a minimum of 120 F at the vent or radiator, and often even hotter than that. It feels nice and toasty, but more importantly it can cover up flaws with your home’s insulation. This is especially true for radiators, which directly warm your walls and not just the air.

Heat pumps run milder; cold climate models max out at 120 F and go down from there, while basic single-stage heat pumps only run at 90 to 100 F. That’s enough heat to keep your house warm, no doubt, but it takes longer to “catch up” in the mornings, if you set your thermostat back at night. (Some experts recommend not using setbacks at all with heat pumps.) 

And if you enjoy the occasional blast of heat near a vent or radiator, it’s not going to feel quite the same after you switch to a heat pump.

Freedman, the mini split design expert from Massachusetts, has even advised a few of his elderly clients to move some of their furniture after switching to a heat pump. A couch that’s against a poorly insulated wall, and especially near a cold corner, might be a lot less comfortable without radiant heat nearby to cover up the drafty feel. 

This furniture-moving step is the exception, not the rule. Upgrading your insulation is generally a very good idea, anyway (and some rebate programs actually require the step before they’ll give out free money for installing a heat pump). But it points to a real difference in how the heat sometimes feels.

Just-OK dehumidifying

Mini-splits (and high-efficiency heat pumps in general) tend to be just OK at dehumidification. It’s a side effect of their super-efficient energy use: A mini split’s indoor coil doesn’t get as cold as a basic AC’s coil, so moisture doesn’t condense onto it as readily.

Mid-summer, you’ll be fine, because it’ll be hot enough that the mini-splits will run constantly. Since they’re always cooling, they’re also always dehumidifying. 

The trouble can come during the shoulder seasons: The temperatures aren’t very high, but the dew points are. Whatever small amount of cooling you need won’t keep the mini-split running long enough to keep the moisture in check. 

All that said, whole-house mini splits aren’t very common in the parts of the U.S. (like the South) where this is a huge problem. If you’re in New England or a similar climate, high dew points in the fall and spring just aren’t very common (and whole house mini splits are common), this might only matter a couple days per year. 

Two easy solutions: You can either pick a mini-split with a Dry setting, which dehumidifies but also reheats your home a bit to keep the temperature steady. Or you can just buy a standalone dehumidifier to use when you need it.

One of the best ways to make sure you're getting a good deal from any contractor is to get multiple quotes. The EnergySage Marketplace makes that part easy. When you sign up (at no cost), we'll share some details of your project (but not your contact info!) with our network of vetted, experienced contractors.

We'll also connect you with an EnergySage Energy Advisor—one of our in-house heat pump experts who can help guide you through the installation process.

And don't forget: When mini splits run off of renewable, zero-emissions electricity from solar panels, they're even better for the environment and can even eliminate your heating and cooling bills entirely. The EnergySage Marketplace can help you find a top-quality solar installer in your area, too.