Mini Split for Garage: Sizing, Voltage, and What to Plan

Why a garage is not a living room of the same size

A ductless mini split is a popular way to heat and cool a garage the central system never reached. There's no ductwork to extend, the head serves just that space, and you can run it only when you're out there. But none of that tells you what size to get. Lots of people shop for a garage mini split and then use a living-room chart, and the garage door is why that doesn't work.

The Size Finder treats “Garage or shop” as its own room type. It adds about 25 percent to the cooling load and uses a higher heating factor, because these spaces are often lightly insulated and the door is a large, leaky surface. That's an allowance, not a measurement of your door. If you've already insulated and air-sealed, say so in the insulation setting. If the door is bare, be honest and don't call the room average.

The picture at the top shows one example: 400 square feet, 8-foot ceiling, average sun, average insulation, mixed climate, cooling and heating. The living room comes out to about 11,200 BTU, and the smallest match is the 19 SEER2 12,000 BTU model (heating nameplate 12,200). The garage comes out to about 13,400 BTU, with heating as the bigger number, and the 12,000 BTU heating nameplate can't cover it. So the tool steps up to the 23,000 BTU system. For cooling only, that same garage is about 11,300 BTU and can land on 12,000. Your climate and your door will change these numbers, so be sure to enter them.

Pick Garage or shop in the free Size Finder. It applies the extra load for a large door and light insulation, then matches a model. The sizing guide explains the same adjustments for an ordinary room.

A garage mini split sizing chart

This isn't a second national chart. It's the Size Finder run on a few sample garages, so you can see the pattern before entering your own. The mini split BTU calculator walkthrough explains the inputs, and the mini split sizing guide has the standard-room chart, including why square footage is only the starting point. If someone quoted your garage in tons, the BTU to tons guide can help. One ton of cooling is 12,000 BTU/h.

Is 12,000 BTU enough for a garage?

Sometimes, yes. A 12,000 BTU mini split is a real match for a garage when the Size Finder lands near that cooling number and you aren't counting on the heating nameplate to handle a colder climate. In the table, the 400 square-foot average garage in a mixed climate is exactly that case if you only cool it. As soon as you add heat, the same example steps up to the 23,000 BTU system.

It's not the go-to for a two-car garage, though. In that mixed-climate example, a 550 square-foot garage at 8 feet, with average sun and average insulation, needs about 15,000 BTU of cooling. A 550 square-foot living room starts at 12,000 BTU on the ENERGY STAR chart. The garage allowance makes up the whole difference. The 19 SEER2 spec sheet’s “up to about 550 square feet” means a typical room, not a bay with a garage door.

Check the class before you grab the less expensive 12,000 BTU box. The 19 SEER2 12,000 BTU mini split delivers 12,000 BTU/h at 19 SEER2, covers up to about 550 square feet in a typical room, and runs on 115V. The 17 SEER2 12,000 BTU mini split publishes 11,500 BTU of cooling and up to about 550 square feet. That's a room range, not a garage range, so it isn't the right choice for a two-car door. And please don't read either model as 600 square feet.

Which model fits a garage

Lots of people search for the best mini split for a garage. The more helpful question is which capacity fits your bay, your climate, and whether you want heat. There's no single best box for everyone.

• A small, shaded, insulated bay that you mostly cool can land on the 9,000 BTU, 23 SEER2, 115V model. Its published coverage is up to about 400 square feet for a typical room, and the garage still needs to check out in the tool.
• A modest bay that the tool puts near 12,000 BTU of cooling, without a heating load beyond the 12,200 nameplate, points to the 19 SEER2 12,000 BTU model.
• A two-car garage, a heating load, or a sunny, poorly insulated door usually points to the 23,000 BTU model: 23,000 BTU/h of cooling, a 22,400 BTU/h heating nameplate, 12,000 BTU/h at 5°F, coverage up to 1,400 square feet, 208/230V, and 17 SEER2.
• DUET pairs two 9,000 BTU heads with an 18,000 BTU outdoor unit, rated 24 SEER2 non-ducted. It's a two-room system, so it's only a garage solution if the garage itself fits a 9,000 BTU head and you have a second room that does too.

If the estimate climbs past 23,000 BTU of cooling, or past the 22,400 heating nameplate, we don't have a bigger single-zone system to offer you. Insulate and air-seal the door and walls, then run the tool again. If it's still over, have a licensed HVAC professional do a load calculation. Please don't put a second head in one open bay and call it zoned.

Where the head and the outdoor unit go

The indoor head works best on an interior wall where it can blow across the bay, mounted high enough to clear a parked car and a workbench, and ideally not aimed straight at the door. The door is the cold draft in winter and the hot slab of metal in summer. The outdoor unit stays outdoors, on a pad or a wall bracket, with room to breathe. It doesn't belong inside a closed garage, because a closed-in condenser can't get rid of heat.

Plan the line-set hole on a wall you don't mind patching, along with a condensate drain that actually slopes away. In a climate where it freezes, a drain that empties where people walk becomes a slip hazard, not just a detail. None of that is refrigerant work. The install planner checks line-set length and mounting against your model, and the delivery and installation guide shows what's in the box.

115V or 230V in a garage

Many garages have a convenience outlet and not much else, and that outlet isn't a dedicated mini split circuit. Our 9,000 and 12,000 BTU single-zone systems are 115V, so even if the tool matches one of those, you still need to confirm a circuit rather than plug in next to the shop light. The 23,000 BTU system needs 208/230V, so if heating bumps your match up to the 23,000 BTU system, that's a panel question too.

We don't list wire sizes or guess at breakers here; a licensed electrician confirms the circuit. Our upcoming 110V mini split guide covers voltage, and the 110V mini split hub lists the 115V models. If you're weighing one garage head against a second room in the house, check out the dual zone mini split guide (and skip the longer extension cord).

Insulation changes the BTU you need

As the last row of the table shows, a bare door can call for more capacity than a 23,000 BTU nameplate can honestly deliver. Insulation and weatherstripping are often the less expensive fix, and they help whatever you buy run less. They don't replace sizing, though. An insulated garage is a milder garage, but it's still a garage. Set the insulation input to match what you actually did, then check the new BTU.

If you only use the garage now and then, that's a point in favor of a mini split. You can heat or cool the bay while you're in it and let it rest when the cars are the only ones there. An inverter can slow down instead of just slamming on and off, which helps in a shop that's full of people one hour and empty the next. It still can't make up for a big miss on capacity.

What you can plan, and what a pro does

Equipment price and install price have their own articles. Our guide to how much a mini split costs covers the equipment, using commonly published US ranges rather than Classic America prices. Labor, the circuit, and the permit are covered in the upcoming mini split installation cost guide. For sheds and bonus rooms without the garage-door problem, see sheds, bonus rooms, and other nonstandard spaces.

Pick Garage or shop in the Size Finder, then check the matched card against the spec sheet. If you're deciding between 12,000 and 24,000, compare models side by side in the compare tool. Prefer to talk it through? Call us at 1-800-349-4360 Ext. 204, Monday through Friday, 10 AM to 3 PM ET.