What type of windows can you use a window AC with?
You can use a window AC with double-hung windows that slide vertically. It’s also possible to buy window ACs that are configured for casement and horizontally-sliding windows but these units are more expensive.
Window ACs sit in an open window with their weight resting on the windowsill and sometimes supporting brackets. They work by moving heat out of your home through a system of refrigerant coils that are more complex than it makes sense to explain here.
The reason why window type matters for installing a window AC is that you want to create a seal between the unit and an open window. Vertically sliding double-hung windows are a great fit because you can close the window tight to the top of the window AC. Then, you only have to attach a window kit to close up the openings on either side of the unit to create a barrier to outdoor air.
If you can’t create a seal, then hot air will just come back into your home around the sides of the window AC.
You can buy window AC units that are oriented vertically to fit into horizontally sliding windows. Basically, most window ACs are wider than they are tall in order to fit comfortably under the fixed upper pane of a double-hung window.
A vertically-oriented window AC is taller than it is wide so that it can fit to one side of a horizontally-sliding window.
It’s even possible to buy a window AC designed to fit into a casement window that swings rather than slides open.
A casement window presents two problems. The first is that the base of a casement window is usually not designed to support the weight of a window AC. Second, it is a lot harder to create a seal against the top of an open casement window because the open window is at an angle.
There are two steps you need to take to properly install a window AC in a casement window. First, you need to build a support platform that can accommodate the weight of your window AC. You can do this partly using the redundant support system that will come with a casement window AC.
This support platform includes a metal brace called a platform assembly that you’ll need to install on the outside of your house. You’ll then need to make your own support base out of wood that will rest on the indoor windowsill.
The casement window AC should sit so that it just clears but does not touch the bottom sill of the window. Normally the bottom sills of casement windows are not designed to be load-bearing so its best not to put any weight on it.
The other step is to secure a seal against the top of the casement window with plastic board. Most casement windows will swing all the way out so you can fit a flat screen against the upper part of the window frame.
One downside of this approach is that more of your window space will be covered with plastic board or a window kit than if you were installing a window AC in a double-hung window. This means you’ll let more heat in.
Mark is a journalist who has written about home products for two years. He holds a masters degree with distinction from the London School of Economics and an undergraduate degree from the University of Edinburgh.