I made this mistake years back, and now my friend made the same just this week. He bought us an air conditioning unit for our apartment due to the scorching (spring!?) heat. Unfortunately, he didn’t know that you cannot use an outdoor (window mounted) A/C unit for indoor use (I wasn’t informed about the purchase until I saw the unit at home).

Not only that, it’s impossible to mount the thing since the width of the window is smaller than the width of the unit itself.

So, I want to inform you about why there is a huge difference between an indoor and an outdoor unit.

Outdoor Unit

The outdoor unit, aka the window mounted unit, is meant to be mounted through a window (1/2 of the unit sticks out the window) so the heat generated by the unit can exhaust outside.

My friend and I tried running the outdoor unit, indoors, to discover that more heat was generated from the unit compared to the cool, conditioned air. So, rather than the room temperature going down, it actually rose a few degrees before I decided it wasn’t a good idea to keep running it.

Basically, an outdoor (window-mounted) A/C unit requires outside exposure to exhaust the heat generated from generating cool air.

When you go out to buy an A/C unit for the first time, you’ll be tempted to buy the outdoor unit and assume it can be used indoors because it’s significantly cheaper (outdoor vs indoor) compared to the indoor units.

Indoor Unit

The indoor unit (aka portable A/C unit) does not require window-mounting at all. The unit still does generate heat as it makes the cool air, but there is a flexible pipe that goes out from the unit which routes the heat to the outside through your window.

Notice the hose in the picture, you just drop the hose through your window for the heat to go out.

Anyways, I hope this article will serve you well on your A/C purchases. Don’t repeat our mistakes!