Can you Cool a Garage with a Portable Air Conditioner?

I’d love to spend my free summer days fixing a classic car in my garage. But living in Florida, my garage quickly becomes unbearable during the hot summer days.

I started looking into different ways of cooling down my garage and one of the first things to come to mind was a portable air conditioner.

Can you cool a garage with a portable air conditioner? Yes. A 7,000 BTU air conditioned should be enough to cool a 1-car garage, while a 2-car garage would need a 12,000 BTU air conditioner. However, it’s important to have insulation so the cold air doesn’t escape.

While I was digging into this, I found out a few things that surprised me. I’ll get into those in a bit, but first, let’s talk about why it’s so hard to keep your garage cool in the summer.

Why Is It So Hard To Cool A Garage?

Garages are usually the most exposed room in your house. There’s a lot of empty space and they usually don’t have any sort of insulation – especially on your garage door.

That, along with the complete lack of windows to help with air flow, can make the garage unbearably hot at times.

Additionally, depending on its construction’s materials and location, the temperature inside your garage can be 10°F to 18°F (5°C to 10°C) higher than outside!

Your garage will transfer heat through the ceiling, walls and even your doors (especially the garage door itself). If you don’t have adequate insulation in your garage, any cooling you do will just leak to the outside air.

Problems With Using Portable Air Conditioners In Your Garage

There are other problems with using portable air conditioners in your garage.

At a VERY high level, an air conditioner brings in warm air through an inlet valve, cools it down and sends it into your room. The warm exhaust air is then kicked back outside and the process starts over.

For more details, I really recommend this video from Technology Connections. Nobody is ever going to say that digging into how portable air conditioners work is exciting stuff, but he at least makes it interesting.

The point I want to make is that the exhaust air needs to go somewhere. If your garage doesn’t have a window or a vent that you can connect the air conditioner to, then that air is just going to go right back into your garage.

That may actually increase your garage’s temperature instead of lowering it.

Finally, as I said before, if your garage isn’t insulated, all that cold air will just bleed through to the outside.

All that said, in some cases, a portable air conditioner can be the right solution. It just takes a little knowledge to pick the right one.

How to Choose the Best Portable Air Conditioner For Your Garage

Garages come in all different shapes and sized. The bigger your garage, the stronger air conditioner you need.

Before you start shopping for a portable AC unit, you need to figure out what size you need.

What is a BTU?

You may have heard the term BTU’s before. BTUs, or British Thermal Units, are an internationally used unit of measure for energy.

One BTU is the quantity of heat required to raise the temperature of 1 pound of water 1 degree Fahrenheit at a specified temperature.

However, for air conditioning, that’s not the definition everyone uses. They like to keep you on your toes.

When you see BTU’s listed on an air conditioner, it’s instead referring to the amount of heat the device can dissipate in one hour from a determined room.

That means you’ll need a different BTU rating depending on the size of the room you’re trying to cool down. Keep in mind that a higher BTU rating will almost always mean a larger, heavier, and more expensive air conditioner unit.

How Many BTU’s Do You Need To Cool Your Garage?

Most portable AC units range in strength from 8,000 to 25,000 BTUs. For most two-car garages, I recommend buying a unit with at least 12,000 BTUs.

This chart, taken from, shows the minimum number of BTU’s you would need to cool your room.

Area To Be Cooled (square feet)Capacity Needed (BTUs per hour)
100 up to 1505,000
150 up to 2506,000
250 up to 3007,000
300 up to 3508,000
350 up to 4009,000
400 up to 45010,000
450 up to 55012,000
550 up to 70014,000
700 up to 1,00018,000
1,000 up to 1,20021,000
1,200 up to 1,40023,000
1,400 up to 1,50024,000

Now keep in mind that this chart assumes a well-insulated room. Unless you have insulation in your garage, you may want to bump up to a higher BTU output air conditioner.

Other Cool Features

Aside from the strength, there are a couple of other factors to consider when shopping for a portable air conditioner for your garage. Here are a few of the most important ones:

  • Size – Your garage is probably cramped as it is. All other things being equal, look for the unit that takes up the least amount of space possible.
  • Timers or Remote Controls – The temperature of your garage will change throughout the day. A unit with a timer can let you set the air conditioner to cool down your garage at the same time every day. Similarly, a unit with a remote control can let you manually turn on the AC before you start working.
  • Mobility – Air Conditioners aren’t light. If you are planning on working on different projects in your garage, ensure that your unit has wheels.
  • Dehumidifier – I’m a big fan of garage dehumidifiers. If you have the option of buying a portable air conditioner with a built in dehumidifier, I highly recommend it.

Other factors you need to consider

Even the best portable air conditioner will have it’s off days. Its efficiency will fluctuate depending on the weather outside and even how your garage is built.

Here are some other things to consider before deciding on a portable AC unit for your garage:

  • Your area’s climate – If you live in an area that gets extremely hot and\or extremely humid, you may need to look at a larger portable AC unit to compensate.
  • How often you use your garage (and how) – If you use your garage primarily for storage, you’ll need a smaller size air conditioner than you could if you were welding or using power tools that give off a lot of heat. If you need a colder environment for long periods of time, you might need to consider a more permanent solution.
  • The design of your house – If you have living space above your garage, air conditioning your garage could lower the temperatures of other areas of the house.
  • The garage design – A portable AC needs to vent the hot air. If your garage does not have any windows, you might be able to drill a hole in the ceiling or walls (if you’re comfortable doing that). Otherwise, you’d need to crack open the garage door which will also let some of the cold air out.

Tips to Help Your Portable Air Condition Cool Your Garage

In addition to garage fans and air conditioning, there are a few other tips and tricks that can help you keep your garage cool. Some depend on how your garage is built, but others are more general.  

Here are a few of the best tips for cooling your garage:

  • Park your car outside the garage for a few minutes: A standard car’s engine runs between 195°F to 222°F (95°C to 105°C). That kind of heat makes it hard for your air conditioner or garage fans to work. Allow your car to cool down a bit before you bring it inside and you’ll save your air conditioner a lot of work.
  • Use lighter colors: When choosing what color to paint your garage, pick a lighter color. A black or gray garage may look cool, but those colors absorb heat while lighter colors like white will reflect heat.
  • Increase air flow: Keeping your garage clutter-free can help increase air flow. The more the air has to move around stacks of boxes and cabinets, the less it can cool the air around it. Install cabinets and shelves to optimize the space and allow as much air to flow as possible.
  • Choose the best time to work: Consider timing your work so you’re there during the early morning or late afternoon when temperatures are lower.


A portable air conditioner is a fairly inexpensive way to cool off your garage, and it’ll definitely get the job done. The next step is to look at your own situation and decide if you need to air condition your garage or if you can use fans instead.

For more on this, check out my article asking if you should air condition your garage. It goes into some of the reasons why you should and some reasons why you shouldn’t.

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