We get this question from customers frequently. Will it work? The short answer is that it is possible. The long answer is that, in most cases, it is very difficult for a portable air conditioner to be effective in cooling a garage.
There are several reasons as to why cooling a garage is more difficult than a room in a house. The first (and biggest) reason is that most garages are not insulated. An uninsulated garage does not hold the cool air in or prevent the hot air entering from outside. This creates an extremely high heat load that is typically more than a portable air conditioner can handle.
"I have a small garage. Won’t the most powerful air conditioner work?"
This is a common assumption. When trying to determine the BTU level appropriate for your room size, the square footage and heat load must be considered. A higher BTU is recommended for a smaller room if the heat load is larger. However, in the case of garages, the heat load can be more than anticipated. More often than not, a portable unit cannot handle that heat load. This is especially true if the cooling is started during the peak high temperature of the afternoon.
Sometimes a more powerful unit will be able to bring the temperature down, but there are still a few reasons why we still do not recommend using a portable unit in a garage. In order to achieve the desired cooling, the unit has to work extremely hard. It might cool the garage temporarily but the room will not be able hold that temperature. It will quickly heat back up, and the unit will need to cycle on to bring the temperature down once again. This quick on/off performance of the air conditioner leads to an overworking of the compressor. It’s known as short-cycling, and because it is not operating to its intended use, the compressor’s life will be reduced.
Issue of Venting the Portable Air Conditioner
The air conditioner must vent the hot air somewhere. Garages usually do not have a traditional sliding window, which is the most common way to vent a portable unit.
If a window is not an option, the other choices would be venting through the roof or wall. This would require drilling a hole through the side of the garage to fit the exhaust hose. This is not a viable option or desire for most people.
But, is it possible?
Again, it is not recommended, but yes, it is possible.
If you live in the northern half of the country where the highs might be 90° F, your garage has an insulated roof and walls, and you have a way to vent the exhaust hose, it could be possible.
If you live in the southern half, where the highs are above 100° F and the garage is not insulated, then it’s not worth attempting.