Best Portable Air Conditioner for a Garage, and When to Skip One

A portable air conditioner is a narrow buy for a garage, and owners who tried one report more complaints than praise. Here's how it went for the owners who said:

That doesn't make a portable the wrong buy, just a narrow one: the rented garage you can't drill, the HOA that won't allow a hole or an outdoor unit, the garage you need cool for one project a year. For those, the type matters more than the brand. We'd buy a dual-hose inverter unit like the Whynter ARC-1230WNH or the Midea Duo, set your expectations by its SACC rating, and do the venting and drainage properly. If you own the garage and want a cool shop all summer, skip ahead to the mini-split section.

When a portable makes sense in a garage

People land on a portable for a short list of reasons, and each one is legitimate:

• You rent: a portable leaves with you; a wall sleeve or mini-split stays with the house. Renters ask how to vent a portable in a rented garage, including one turning a windowless attached garage into a home office.
• Your HOA or your house won't take the alternative: one Arizona owner's HOA wouldn't allow a hole in the garage door, and a second wasn't sure theirs would allow a mini-split.
• You need cooling a few days a year: a garage used as a temporary repair shop once a year or so, one needed for a handful of days, or a unit that only runs during oil changes and projects, then rolls to the corner.
• It's temporary: one shopper wanted cooling for about a year in a garage office and had no room left in their electrical panel for a new circuit.

We'd skip a portable when:

• You own the garage and want it comfortable from June to September: a mini-split or a window or through-the-wall unit keeps the compressor's heat outside, and you'll run it enough for the difference to matter.
• The garage is three cars or bigger: or uninsulated and in full sun. The capacity math below doesn't work.
• You also want winter heat: the heat-pump portables we cover stop short of garage winters (more below).

One hose or two: why it matters more in a garage

Buy dual-hose. A portable carries both halves of an air conditioner in one box. The cold coil cools your air; the hot coil, the condenser, needs air blown across it and sent outdoors. A single-hose unit uses your garage air for that and blows it out the hose. That air has to be replaced, so outside air gets pulled in through every gap, and a garage has plenty: the big door's edges, the attic hatch, the walls the house shares. One owner on an older single-hose unit had an architect explain negative pressure to them, and says it doesn't get the garage to a workable temperature. Another's old single-hose unit drew heat from the attic and put heat and humidity into the walls and cabinets of the house.

A dual-hose unit pulls outdoor air in through a second hose to cool the condenser and sends it back out, so it isn't exhausting the air you paid to cool. Midea describes the Duo's hose-in-hose duct as one that exhausts hot air and brings in outdoor air. It isn't a perfect seal on the building, though. One owner with two dual-hose units says they still create negative pressure, and the South Florida garage that only dropped 3°F had a dual-hose inverter. That owner measured the hose at 85°F and a 95°F hot spot near the condenser inside the garage. Even with two hoses, the hot side of a portable is still inside your building.

In a garage, the hose layout also decides how hard the venting is. The Whynter ARC-1230WNH and the Midea Duo both run intake and exhaust through one oval hose-in-hose duct. That's tidy in a window kit and awkward through a wall or a door panel. One Duo owner couldn't find a vent for the oval duct that their household would accept and ended up using an older single-hose unit. For a wall install, a box that splits the duct into two 6-inch round ducts works, as long as you don't neck it down below the factory size. If you need two separate round hoses, Whynter's ARC-147WF has them, but Whynter lists no inverter for it and its CEER is 7.83, about half the ARC-1230WNH's 14.2. We'd still buy the inverter and build the adapter.

Read the SACC number, then do the garage math

Portables carry two cooling numbers, and the box leads with the bigger one. The lower one is the SACC rating from the DOE's 2017 portable test. The Whynter ARC-1230WNH is 14,000 BTU on the ASHRAE scale and 12,000 BTU SACC. Midea markets the "14,000 BTU" Duo with heat (MAP14HS1TBL) as 12,000 BTU DOE in the US. Whynter's older ARC-14S is sold as 14,000 BTU ASHRAE and rated 9,500 BTU SACC. Shop by SACC, and know that 12,000 is the most any portable we cover is rated for.

ENERGY STAR's sizing chart for room air conditioners is the closest published yardstick, and it's a generous one for a garage because it assumes an 8-foot ceiling and an ordinary room. Here's what it asks for in typical garages, using our example dimensions:

Paper is the best case. ENERGY STAR itself says rules of thumb typically result in incorrectly sized equipment and points to a Manual J load calculation. A garage with a west-facing steel door and an uninsulated roof isn't the ordinary room the chart assumes, which is why insulating and sealing the door comes first. Owners credit an insulated or sealed door with a big difference; one, with a sun-facing wooden door, found the inside of it hot to the touch on a 75°F day until they switched to an insulated door.

Then check the temperature range. Midea's Duo manual lists cooling operation from 60°F to 95°F. Whynter's ARC-1230WNH manual says 60-95°F in one section and 63-90°F in another. Garages run past that: owners report 106°F inside on a 95°F day, and 95-100°F when it's 105°F out. Whynter's troubleshooting table lists a room outside the unit's operating range as one reason the fan runs but the compressor doesn't start; Midea's manual doesn't say, and we won't guess. Either way, a portable you switch on in a 105°F garage is outside the conditions its maker lists. The Dallas-area owner's routine is worth copying: crack the door with a fan pulling outside air through until the garage is near the outdoor temperature, then close up and run the AC.

Venting a garage with no window

Both hoses have to end outdoors, sealed, and within the length the manual allows. Whynter lists the ARC-1230WNH's hose at up to 47 inches and the ARC-14S's at up to 60. One shopper who hoped to run a hose up to a ceiling vent found the unit's 59-inch maximum didn't reach the ceiling. Don't extend past what the manual allows, and don't count on the stack effect to help once the hose is sealed to the vent. The routes that work, roughly from least to most permanent:

• A window, even a casement. The Duo's kit fits openings from 19.1 to 63.8 inches, and the ARC-1230WNH's kit runs 28-82 inches with a 9.5-inch-wide panel. One owner had an acrylic panel cut to fit their garage's crank-out casement window with a port for the Duo's hose.
• The side door. Swap the door for a plywood-and-rigid-foam panel with holes for the hoses. One owner who needs garage cooling about once a year rigged tarps and curtain rods instead and says it didn't work great but got them through.
• Under the big door. A strip of duct board under a partly open door, or a short stub wall the door closes onto, with the hoses through it. If the top of your door gaps when it is partly open, the garage will not hold its cooling. One Whynter owner runs 4-inch duct to slot vents under the door; we would keep the factory duct size instead.
• Through the wall. If you own the place, a round hole with an exterior wall cap per hose is the cleanest result. We wouldn't do it on a rental, and one homeowner turning a garage into a workspace worried that two holes through brick would hurt resale.

Two routes we'd avoid. Don't vent into the attic. You'll read that it can work; we disagree, because an attic is designed to vent only so much heat, and humidity is the other problem. These units are designed to evaporate condensate into the exhaust, so you'd be blowing hot, wet air into a space built to shed heat. And don't connect a hose to an existing vent or pipe in the garage wall or ceiling until you know what it serves. One homeowner found what looked like old metal appliance chimneys and a combustion-air intake. If a gas water heater or furnace uses an opening, it isn't yours to borrow; have a licensed pro look at it.

Where the water goes

Plan a drain before the first humid week. The Duo and Whynter's dual-hose units are designed to throw cooling-mode condensate onto the hot condenser and blow it out with the exhaust. In dry weather that works. In humid weather it often doesn't keep up: in our Midea Duo review more than half a dozen owners drain by hand. Constant draining can also be a defect. A Whynter ARC-14S owner in a 150 sq ft Florida workshop was draining multiple times a day until they found the splash motor had come disconnected at the factory; once it was plugged in, they got through the whole summer without draining. A garage adds a twist: there's often no floor drain, and the unit sits on a slab.

Your options, cheapest first:

• Empty the internal tray by hand: fine for a few hot afternoons in a dry climate, a chore in a humid one.
• A gravity hose: Whynter says to attach a hose to the ARC-1230WNH's upper drain port running downward to a floor drain or bucket. One owner raised their garage unit off the floor so a hose could drain it continuously. Under the garage door to the driveway works if the hose runs downhill all the way.
• A condensate pump: for when the water has to go up or across the garage. Set it below the drain port and run its line out.

The Little Giant VCMA-15ULS moves 25 gallons an hour at 10 ft of lift and shuts off at 15 ft. Its manual wants the pump on its own circuit, with no other receptacles or equipment on it and nothing that runs intermittently, and no extension cord, which in a garage usually means a new circuit. Its overflow switch is built to open a low-voltage control circuit, and a plug-in portable usually has none, so on this setup the switch is mostly an alarm option. Our condensate pump guide covers the rest. Both picks also need a drain hose in heat mode: Whynter's built-in pump on the ARC-1230WNH only runs when heating, and Midea's manual requires the drain hose in heat mode.

Water left in a warm cabinet grows mold, and a garage unit that sits in a corner for weeks between projects is a candidate. Seven or more Duo owners describe mold or a mildew smell, and one garage shopper ruled out the Duo over those reports. One Whynter owner (an older, fixed-speed ARC-122DS, not our pick) runs fan-only for about 30 minutes before powering off and found the inside clean when they opened it up. For storage, Midea's and Whynter's manuals both say to drain the tray and run fan mode for 12 hours in a warm room. A shorter fan-only run every time you roll it away is our habit, not the makers'. Both manuals also say to store the unit in a cool, dark place because direct sun or extreme heat can shorten its life, so a garage that bakes all summer is a poor place to park it for the off-season.

Power, heat and noise

Every portable here plugs into a 115V outlet, but they draw a lot through it. Whynter lists the ARC-1230WNH at 1,298 W and 11.9 A. Midea doesn't publish an amp figure for the Duo; one retailer lists 15 A for the MAP14HS1TBL. A garage outlet may share a circuit with the door opener, a freezer or the tools you're about to run, so read the nameplate of whatever you buy and ask an electrician whether that circuit can carry it. That's a call we won't make from here.

Don't count on a portable for winter. Midea's manual rates the Duo's heat pump for 41-86°F, and it shuts off when outdoor air reads 41°F or below. Whynter doesn't publish a low-temperature limit for the ARC-1230WNH's heat mode that we could read. For a garage you'll work in through the winter, see our garage heater guide.

Noise matters less in a garage than in a bedroom, unless the garage is your office. Whynter lists the ARC-1230WNH at under 42.5 dB on low, 49.5 on medium and 56.5 on high, and Midea says the Duo runs "as low as 42 dBA." We don't measure sound, and neither maker publishes test conditions we could locate, so don't compare the two figures directly. One Duo owner with a windowless garage shop was amazed at how quiet it is on high; an owner who ran a portable in a basement for years calls portables loud as hell and has since bought a DIY mini-split for their garage.

When to buy a mini-split instead

If you own the garage, the mini-split is the better machine for nearly every job a portable does there. The compressor and its heat sit outdoors, nothing takes up floor space, the water leaves through a drain line, and it heats in winter. Our garage pick, the MrCool DIY 5th Gen 12K, is rated for 12,000 BTU/h of cooling on 115V, makes 8,400 BTU/h of heat at 5°F per NEEP, and ships with a 25 ft pre-charged quick-connect line set. Its warranty allows owner installs, with 5 years on parts and 7 on the compressor, and labor is never covered. Its efficiency is rated in SEER2 (23.5), a separate DOE test from the CEER portables publish; we know of no official conversion between them.

The catch is the circuit: it calls for an 18 A minimum circuit ampacity and a 20 A maximum breaker, which is an electrician's job and possibly a permit. Our garage mini-split guide walks through sizing, placement and the install, and our 115V mini-split guide compares the plug-voltage options. Garage mini-split owners generally find a 12K or smaller enough for a one- or two-car garage or a shop of about 300-500 sq ft. Several people who tried portables have gone or plan to go that way: the South Florida owner planning to return their dual-hose unit, the basement portable owner who bought a MrCool 12K for a 375 sq ft garage, and the Dallas-area owner if they stay in the house.

If you can cut a wall but don't want a split system, a window or through-the-wall unit also keeps the hot side outdoors. Owners who cool a garage or shop with one are mostly satisfied; one says theirs is so loud they'd have gone mini-split. Our through-the-wall AC guide covers the sleeve units, and our window AC vs portable AC guide runs the efficiency numbers between the two types.

What we'd put in your garage

• Rented or HOA garage, two cars or smaller, cooling only: the Whynter ARC-1230WNH, vented through a window, a door panel or under the door, with a drain hose. Check that the seller is an authorized Whynter dealer, or the warranty doesn't apply.
• Same garage, and the Whynter is unavailable: the Midea Duo with heat (MAP14HS1TBL). Same 12,000 BTU SACC and the same oval hose-in-hose duct, the same CEER 14.2 in DOE certification records, and a one-year warranty.
• Humid climate or no floor drain: add the Little Giant VCMA-15ULS, on its own circuit.
• You own it and want it cool all summer, or warm in winter: the MrCool DIY 5th Gen 12K on 115V, with an electrician running the circuit.
• Three-car garage or an uninsulated one in full sun: no portable. Insulate the door, get a load calculation, and size a mini-split to it.

Whichever you choose, insulate and seal the door before the first hot weekend; every option here works better for it.