Air Conditioners

Can Window Air Conditioners be Installed Sideways?

Window Ac Unit

During summertime, you will find it difficult to live without a window air conditioner. It has become part of summertime appliances that you have to plan for.

However, it is unfortunate that window air conditioners do not always fit as you would always expect them to. Sometimes, it may look like the only option is to install it sideways.

Window air conditioners should never be installed or turned sideways. While shipping a window air conditioner, there are chances of turning or storing it sideways.

Never attempt to keep it that way. Doing so will affect the function of your air conditioner and may also cause accidents.

This article explains how air conditioners work and if you can install or use one sideways, vertically, or horizontally.

How Does a Window Air Conditioner Work?

Most people would think that air conditioners work by cooling the air in a room, which is not valid. Air conditioners work by removing heat from a room.

The appliance has two sets of coils connected with a refrigerant fluid constantly flowing inside. Its primary function is to extract heat.

You will find the two curlicues at both ends of the air conditioner, whereby one coil sits in the room while the other one is outside.

In extracting heat from the room, the two ringlets work according to the second law of thermodynamics which argues that heat moves from a hot area to a cold place.

The coil in the room is colder than the room temperature, while the one outside the house is hotter. Thus, the room’s air loses its warmth while blowing over the cold coil. The cooled air returns to the room, and the cycle continues until the room is effectively cooled.

How Does the Coil Remain Cold?

The ringlet remains cold despite continuous warm air blown over it because of the refrigerant in the coils. The coils have a refrigerant that is fluid and has a shallow boiling point.

The boiling point is deep that as warm air flows over the coils, the refrigerant heats up, becomes gas, and flows to the outside spiral.

Heat transfer helps the coils to remain cold. Hot gas loses heat and turns into a liquid through heat transfer while the fan blows cold air. Then the liquid goes back to the coil in the room, ready to turn into gas as the air blows over it.

Other components of a window air conditioner help it achieve its function. These include:

  • The evaporator: The evaporator contains the cold coil in the unit in which the refrigerant changes into a vapor.
  • Compressor: Which is used to compress vapor, reducing it in volume. The moisture becomes hot through heat transfer and then leaves the compressor at higher pressure and temperature than the evaporator. Note that the vapor from the evaporator goes to the compressor, where it is compressed.
  • Expansion valve: The expansion valve is placed just before the evaporator. Its primary function is to reduce the condensed refrigerant’s pressure as it moves to the evaporator. The boiling point is low enough to an extent it boils as it absorbs heat from the air, changing into vapor and repeating the cycle.
  • The condenser: The condenser helps turn the heat into a liquid.

What Will Happen if I Turn the Window Air Conditioner Sideways?

Primarily, the components which facilitate cooling would not function as expected. Here are the reasons why you should not turn your air conditioner sideways:

1. The Compressor Will Burnout Leading to a Possible Fire

The compressor uses gears and other parts to compress the refrigerant, already in a gaseous state. Due to continuous movement, you must keep lubricating the moving parts to function effectively. 

Besides lubricating the moving parts, the lubricants act on high pressures and temperatures, which the compressor handles. It is at the bottom of the compressor. 

The lubricants absorb heat from the compressor and can function as a seal. Though the components of a compressor are fixed, gravity keeps the oil at the bottom of the compressor.

Therefore, if the window air conditioner is turned or installed sideways, the compressor and the lubricating oils will turn and flow out. As a result, the components force the compressor to function under intense friction. 

Also, there would be no adequate oil to absorb the thermal energy. Besides, much heat generated by friction from the unlubricated rotating compressor components would continue building up.

In the end, excess heat in the compressor would damage it and worse, cause the compressor to explode and catch fire.

2. Rainwater Can Enter the Air Conditioner

When you look at a window air conditioner, you will notice vents on the sides and the bottom used for ventilation. They are also used to expel heat generated from the condenser.

If you turn the air conditioner on the side, the vents will face upwards. Hence, rainwater may enter the air conditioner, destroying it.

If you cover the vents to avoid rainwater from entering the air conditioner, you prevent hot air from leaving, and hence AC accumulates high heat, which can be disastrous.

3. Condensation May Drain Improperly

Condensation involves moisture or vapor in the air turning from gas to liquid. Warm air from the room cools down while blowing over the evaporator.

It will lead to the warm water condensing droplets on the evaporator’s coils. The droplets then fall because of gravity and are picked by the condensation pan and transported out of the air conditioner by the condensate drain line.

Therefore, if you turn the window air conditioner sideways, you will interfere with the condensation process because the condensation will drip into the air conditioner, destroying the unit and, in some cases, leaking into the walls of your home.

Installing a Window AC for Windows that Opens Sideways

Some window air conditioners can fit into a double-hung, enabling them to open sideways. There are six easy steps to install air conditioners that open sideways. 

First, let’s state the equipment that you would need:

  1. Window sills
  2. Deck screws
  3. Saw
  4. Screwdriver
  5. Plywood scrap 

Steps by Step Guide on Installing Air Conditioners Sideways

1. Take Measurements

Take the air conditioner width measurement. While taking the sizes of the air-conditioner, remember to include the vents on the side.

Placing vents on the side allows the air conditioner to slide in. Also, measure the height of the air conditioner. This height is the box height. It does not involve the lips on the air conditioner’s top and bottom.

2. Cut the Lumber Frame

Cut your 2X4 as 3-width of the conditioner and 2-for the window frame height. Remember the measurement of the air conditioner should include the vents.

3. Begin Working on the Frame

Put down the shorter piece of the 2X4 and screw the ends of the longer pieces to the ends of the shorter one. Then create a rectangle by screwing another short piece of 2X4 within the long parts at the other end.

At this point, it would be wise to put the rectangle into the window opening to check if it fits. It should be able to slide in and sit against the window framing. In case the frame is loose, you can adjust it.

4. Finishing the Frame

Set the window AC into a frame with the bottom lip against the outside of the frame. It will allow the window AC unit to open sideways. After this, you will notice the top lip is u-shaped while the backside is shorter.

Your last 2X4 piece should sit across the top of the shorter leg at the top of the air conditioner. Do not screw in until you have fitted everything to avoid adjustments needed later.

To realize the placement of the 2X4, lean the air conditioner for the front vertical piece of the top lip to lie up with the front edge of the wood frame. That will give you a view of how the air conditioner will look in the frame when complete. 

Also, hold the air conditioner in place and look at the whole configuration to ensure it leans back effectively. An air conditioner should drain and tip away from the window.

Lay a piece of lumber and mark its position on the frame. Then remove the air conditioner from the shape and screw the piece firmly. Also, try to dry-fit the air conditioner into the frame to ensure you have not messed up.

5. Cover the Top of the Frame

Measure the opening on the top of the frame for the plywood covering the hole. Ensure that the wood pieces cannot mount below the long horizontal mark you made in the last bit of 2X4.

Then screw the plywood covering in place. Staple the screening material on the side of the outside facing the frame. Hinge the piece of plywood over the opening and install a latch for it. It will enable you to open the AC from outside whenever you want.

6. Installation

After ensuring everything works perfectly, open the window and slide it inside against the framing.

For more stability to the installation, screw the frame into place by running long screws within the wooden frame and into the structure around the window opening. At this point, you finished installing your window air conditioner in a way it opens from the outside.

Can You Put a Horizontal Air Conditioner in a Vertical Window?

No, you cannot put a horizontal air conditioner in a vertical window. It is recommended to put an air conditioner in a vertical window only when it has a vertical design. Besides, the window slides must open from side to side and not up and down.

You cannot also turn the air conditioner on its side to fit a window. By doing this, you will eventually destroy the appliance.

Dangers of Installing a Horizontal Air Conditioner in a Vertical Window

If you have a horizontal air conditioner, its structure does not allow you to install it in a vertical window by turning it on the side. If you do this, you will quickly burn the compressor inside the unit, destroying it.

Also, the oil and the Freon used by the compressor will flow out. Lastly, the air conditioner should drain condensation to enable cooling. Turning it on will then stop the process interfering with the air conditioner’s functionality.

What Are the Possible Solutions?

1. Pair a Regular Air Conditioner with a Sliding Window

You can solve the problem of a horizontal air conditioner on a vertical window by pairing a standard air conditioner with a window that slides side to side. You can only achieve this when the air conditioner’s width fits the window.

Make sure to slide the window open as wide as possible and measure the opening using a tape measure. Also, measure the air conditioner’s width and check if the space can accommodate the unit. If it is okay, double-check the air conditioners’ height and the window opening height.

Then cut a sizable plywood piece that can fill the open gap between the air conditioner and the window. Get a piece of plywood enough to fill the gap between the air conditioner’s top and the window opening top. 

If you only have this window, cut out a space in an exterior wall of a wood-framed house and then install the air conditioner via the wall. This may not be viable for you if you have a brick building or a rented apartment.

2. Casement air conditioner

A casement air conditioner fits into the vertical space of a significantly narrow window opening. Install the unit on the window frame, which a casement air conditioner should sit on for support.

With a casement air conditioner, you will notice an open space between the top of the unit and the top of the window opening. To get rid of this space, cut a plywood piece the same size and use it to seal the area.

Always make sure you do it correctly when installing a regular window air conditioner or a casement window air conditioner in a vertical opening. Ensure it drains effectively – it is well lubricated and ventilated to avoid problems in the future.

Can You Put an Air Conditioner in a Horizontal Window?

Yes, you can install an air conditioner in a horizontal window. A flat window implies a window that slides left and right instead of up and down. Installing an air conditioner in a horizontal window is similar to installing an air conditioner in a vertical sliding window.

 Steps in Installing a Conditioner in a Horizontal Window:

  1. Before purchasing your air conditioner, choose the window you would install it on and take measurements.
  2. Cut a strip of weather-stripping the same size as the window opening. Remove the adhesive backing from the weather-stripping and adhere it to the windowsill. Ensure the weather-stripping firmly sticks to the windowsill.
  3. Provide a support bracket to the windowsill using screws and an electric drill or screwdriver. Ensure the bracket top is tilted back about ¼ inch and ½ inch. This will ensure once the unit is placed, it can effectively tilt.
  4. Provide a support bracket on the exterior siding with screws by use of a screwdriver or electric drill. The exterior of the bracket may attach directly beneath the windowsill or under the window. This would depend on the size and weight of the unit.
  5. If necessary, assemble the air conditioner. However, you will likely need to attach air conditioner guides on the sides and the top of the unit.
  6. Take the measurements of the side guides and cut a weather-stripping or an equivalent length.
  7. Measure the sliding window height and subtract the size of the unit. The difference would be a gap you would cover using a plastic curtain.
  8. Ensure the window is well-positioned in the window opening and supported using the bracket.
  9. Make holes through the unit’s bottom guide into the window track. Next, insert screws into the holes and screw in a while, attaching the team’s bottom to the window.
  10. Position the L brackets (which come with the unit) to meet the jamb. Make a hole through the hole of the L bracket and into the window frame.
  11. Lastly, plug in the unit.


As we have seen above, you cannot install a window air conditioner on the side. If you attempt to do this, you will interfere with the air conditioner’s functionality, which is hazardous. Always follow the guidelines effectively to avoid future problems. 


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.