No Air Ducts? No Problem

If you want to cool or heat specific rooms with better efficiency and less clutter than window ACs and space heaters—and less complexity than central HVAC—consider a mini-split system. 

Central HVAC usually forces air through several rooms—or the entire house—often heating or cooling rooms that aren’t even being used. The perfect analogy: If you turn the water faucet on in the kitchen and every other water faucet turned on throughout the house…how efficient is that? That’s what central systems do.

Mini-splits are popular as retrofits into existing construction, for a reason that also happens to be another big source of their efficiency: They don’t require costly ductwork. This means they’re much easier to install than a traditional ducted HVAC system, and they can deliver more of the conditioned air they produce, too.

Another appealing factor about a mini-split is a lot of flexibility in sizing the system to your needs. The system consists of two types of units: one outdoor condenser and the individually controlled air-delivering indoor units, which you have at least one of (or, maybe, four). These connect by a refrigerant line and a drain line. The indoor units vary in size based on what the room needs, and they’re typically mounted high on a room’s wall and are about the size of a long duffel bag. 

Some indoor units can also be mounted on the floor or recessed into a ceiling. The ceiling units are more discreet, but they require a much more invasive installation. The outdoor unit can be as small as a piece of luggage, but the more indoor units you have, the larger the outdoor unit needs to be to support them.

Mini-splits offer a lot of control, too, beyond their ability to be programmed like a regular thermostat. The best models can sense when someone is in the room (or not) and adjust the temperature accordingly, and then they can direct the air either away from you or toward you based on your preferences. Most models include a wireless remote and/or a wireless wall-mounted controller, and many can be controlled via smartphone or be integrated into a larger system like Nest or Alexa.

Mini-splits are never cheap. A typical mini-split install costs anywhere from $7,000-$14,000. If you’re looking to create a whole-house system—which needs multiple indoor units and a larger outdoor unit to support them—it can start getting cost-prohibitive. A Service Legends Comfort Advisor can provide you with your best options based on your needs and budget – schedule free estimate.

You also have to commit to a location with the indoor units, and there’s no moving them around, like with window air conditioners or portable ACs. Ideally, the pipes go through the wall directly behind the unit, where they’re hidden. Depending on how the wall is constructed, this may cause the unit to be off-center on the wall, which you may not want.

Even in the perfect location, mini-split indoor units take up a chunk of wall space and they’re not the most attractive things in the world, as we heard separately from two friends who recently installed them. It’s basically a boxy rectangle on your wall. Some manufacturers offer a variety of colors, at least. Another option is to get units that recess into the ceiling. But a ceiling installation will likely be more expensive and invasive.

Mini-splits can also struggle in extreme temperatures. The best systems can operate at 100 percent capacity all the way down to an exterior temperature of about 23 degrees and will even operate at 75 percent at negative 13 degrees. Still, it’s something to consider when setting up a system for your home.

A related (more avoidable) downside is winding up with a system that feels undersized for your needs. To play it safe, an installer might suggest going with a bigger outdoor unit, which has the flexibility to serve multiple indoor units. But the costs add up fast, and it can be tempting to try to get by with the minimum equipment possible. That may backfire if the system is underpowered.

Last, mini-splits are nice in that they are all-electric (and require no additional fuel or gas service, like with some traditional HVAC systems), but their electrical requirements are considerable.

Mini-splits can work as a small space’s primary system in a mild climate, but more often they’re ideal for rooms that don’t already have a heating and cooling system—like an addition, finished basement, attic bonus room, or a garage workshop. They can also add air conditioning to a high-traffic area like a kitchen or living room, or even a room where you just might want a little extra temperature control like a nursery. 

For some homes, a couple of well-placed indoor units can handle the heating and cooling needs for most of the year.

All these advantages of a mini-split add up to increased comfort, especially when compared to the (much more affordable) options for treating single rooms: window air conditioners and portable ACs.

For one, mini-splits are much quieter. With the system split between an indoor and outdoor unit, the only noise in the room is the fan needed to move air. There are none of the loud compressor hums that is typical of a window unit. In addition, most quality mini-split systems, much like the best whole-house systems, use variable-speed motors in their compressors. On a mild day, a mini-split will actually run on a slower speed than on a hot day and save you energy, where a window unit will just come on and off on and off. This constant cycling of the window unit consumes a massive amount of energy. Think of it like trying to push a car from a dead stop to 5 mph versus pushing it as it’s already rolling forward. Which one requires more energy? The variable speed motors in a mini-split are never at a dead stop.

Another downside to window units is that every time that air conditioner shuts off and stays off for 20 minutes, you’re not doing any kind of dehumidification. Since the mini-splits variable speed can dial down to near zero once the target temperature is reached, it’s actually at its most efficient when you leave it at the setting you find comfortable—win-win.

Beyond variable speed, a mini-split is comparably more efficient than a window unit due to its different construction. Within the housing of the window AC are the same two components of a mini-split—the evaporator and a condenser. Those two components of that system are separated by a very thin wall, and that thin wall is not doing a great job of keeping heat energy out. With a mini-split, the two components are now separated by your insulated wall.

The way a mini-split disperses air is better than a window unit or a portable AC. When you’re trying to blow cool air into a hot room, the cool air will fall, so a window unit has a tougher time driving that cool air across the room because of the position of the window. A mini-split is typically mounted high on a wall or even in a ceiling, giving it a much better throw of that cool air, with the ability to disperse it in a sweeping motion from side to side, up and down, or even directed towards a wall, if you want some circulation without a direct blast of air.

Last, a mini-split doesn’t occupy a room’s electrical outlet or affect the function of your windows. A window AC completely blocks a good chunk of the window, obviously. And even a portable AC hogs its share of the window space by requiring the window to stay shut tight against the vent hose hardware that every portable AC uses to dump heat outside.