Can You Put A Window Air Conditioner In Sideways? (Why Not + Alternative)

Here is the thing: Window air conditioner doesn’t know up from down, or left from right. Can you put a window air conditioner sideways? What happens if you turn an air conditioner on its side? Let’s think this through and check the best alternative to turning a window AC sideways.

There is usually only one reason why homeowners would consider installing a window air conditioner sideways:

You probably had a narrow window.

In fact, the window is usually too narrow to allow for the full length of the window AC unit to be placed on the window sill.

window not wide enough for window air conditioner
All standard window AC units will fit a wide window. When it comes to narrow windows, we start to think about turning the unit sideways.

The problem with small windows is that window AC units are usually wide (18-20 inches or wider). However, they are not all that high (anywhere from 11 to 16 inches). Example: LG LW1216HR, one of the best-selling 12,000 BTU window AC units, is:

  • 23.63 inches wide.
  • 14.97 inches high.

window ac that cant be turned sideways

With that 23.63″ width, you can’t really fit it into an 18-inch or 20-inch wide window, right? But, if you would flip it by 90 degrees, the 14.97″ height now becomes the new width. In essence, a window air conditioner would fit nicely into a small window if you flip it sideways.

Now, of course, the first question we get and the first question we are going to address is this:

Can you install a window air conditioner sideways?

Will something happen to the window AC if we don’t install it as intended? Well, the refrigerant flow, compressor, fans, and other window AC parts are not gravity-dependent; namely, they should perform equally well if you put a window AC sideways onto a window sill.

Can You Put A Window Air Conditioner In Sideways
Components in window AC unit don’t require gravity (correct position) to work properly.

This is not a topic with a clear yes-no answer and we are going to look into the nuances of actually putting a window AC unit on its side. Even more importantly, however, we are going to look at a special type of thin window AC unit, created especially for the narrow window.

If you already have an existing broad window AC unit, it makes sense to check if you can put it on the window sill sideways. However, if you are buying a window AC unit for a narrow below 20-inch wide window, you don’t have to check if sideways installation is OK. You can just buy a window AC that is already engineered as a ‘sideways positioned’ unit (Example: 14.2 inches wide and 20.25 inches high).

Note: It does seem a bit unnecessary to rotate a window AC if you already have a window AC that is engineered for narrow windows. Usually, the problem is that homeowners are not aware that such window AC units exist in the first place.

Let’s first look at the consequences of turning an AC unit sideways. After that, we will look into these narrow window AC units with widths below 15.5 inches:

Can You Install A Window Air Conditioner Sideways?

If you would put a window AC on the window sill sideways and turn it on, it would work normally. The only thing you need to check is if the airflows are OK. If you block any airflows, it’s not OK to put a window AC sideways. If you check the LG unit in the photo above, you can see that it has openings on the sides; turning such a unit sideways is a definite no-no.

Now, as we have mentioned earlier, there is nothing inside the air conditioner that would actually require the assistance of gravity (refrigerant flow, fans, compressor, fan motor). So why don’t we just put a unit sideways?

3 reasons:

  1. All window AC manufacturers specify how a window AC should be installed correctly. You will find that information in the manual; not one manual states that ‘Yes, you can put it sideways’.
  2. Window AC units are designed to be standing upright. All the supports inside the unit are engineered as if you are going to use a window AC unit standing up; in the correct position, that is.
  3. You can run a window AC sideways for a short time. However, we are not aware of how running a window AC sideways would affect (shorten) its lifespan. As you can see here, window AC units last for about 10-15 years, if used correctly. We just don’t know if running them sideways will cut into the life expectancy.

All in all, window ACs are capable of operating even when installed sideways (given that we don’t block any airflow). However, installing a window air conditioner sideways is not exactly playing it right and is advised against.

This is especially true because – if you are trying to solve a narrow window problem – you can use a special type of window air conditioner that doesn’t need to be installed sideways because it is engineered in a way that mimics sideways installation. Here is this type of AC:

Vertical Window AC Units For Narrow Windows

In a standard window AC unit, the majority of components are positioned horizontally. Evaporator coils run from left to right, condensation coils run from left to right, the fan motor is positioned next to the fan, and so on. That’s why we get the standard wide look of window AC units.

To be able to install a window AC into narrow windows, however, a special type of vertical window AC units were designed. These are called casement window AC units. Their width dimension is compressed as much as possible; that’s why they are higher than standard units.

In casement window AC units, everything is engineered vertically. Evaporator coils run from up to down, condensation coils run from up to down, the fan motor is positioned below the fan, and so on. Engineering a window AC unit in such a way reduces its width and allows us to install a window AC unit in very narrow (up to about 15-inch wide) windows.

sideways window air conditioner
Casement Frigidaire window AC unit with 8,000 BTU capacity. Compared to the LG unit we check above, it is almost 9 inches slimmer.

These units are fairly unknown to many homeowners; that’s exactly why we have quite a lot of people asking us if they can put a window AC sideways. The whole point is that you don’t have to: You can just buy a casement window AC that will fit a narrow window.

We have made an analysis of the existing casement window AC units on the market and made a list of the best of these casement/vertical air conditioners here. You can check them out and check the width dimensions to make sure it will fit your window.


All in all, you are usually physically able to put a window air conditioner in sideways. Is it OK to put it like that? It’s probably not the best idea, especially knowing that you can just choose a casement window air conditioner and you don’t even have to worry if you can put a window air conditioner sideways.

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