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How to Fill an Opening from a Wall AC [5-Step Solution]

It’s very common to have additional openings in your wall while upgrading AC. But not closing the opening afterward can let the cold air escape.

How to fill an opening from a wall AC? 

You will need to measure the opening and cut two pieces of plywood to fit. Attach them to the existing frames. Make sure that the plywood is placed securely from both sides of the house. Spray expanding foams into the gap for remaining openings. Finally, install several pieces of insulation. 

Sounds easy enough? It’s just a brief answer to what you might be looking for. There are plenty of steps that are involved in it. 

Don’t worry. I’ve prepared this descriptive article to solve your problem.

Fill an Opening from a Wall AC in 5 Steps

AC has become one of the basic necessities on warm summer days. We all want one. Also, upgrading them brings massive advantages. 

But one problem that pops up is the left out gaps. Filling up those gaps is a hassle if you don’t know how to. 

Lucky for you, it’s not that hard once you learn it. You don’t need any previous experience for that. Here’s how you can fill the opening from a wall AC:

Step 1: Assess the Opening

Firstly, you will need to measure the size of the opening. After getting an accurate measurement, cut two pieces from the 2-by-4 plywood. Make sure that they fit the opening properly 

Place the pieces that you have cut in the opening. Attach them to the existing frame and use screws to attach them. 

While inserting the screws, start with the bottom part. Drive the nail downwards at a 50-degree angle. Repeat the process again for the upper side frame. 

Step 2: Cut the Drywood and Plywood Pieces 

The height and width needs to be measured in this step. After taking the length and width, cut a piece from the drywall. Fix the jagged drywall seams if necessary. 

Once finished with drywall, cut a piece from the plywood according to the size. 

It’s time to measure up the distance. Get the measurement between both sides of the opening. Then in the midpoint, nail both pieces and place them. 

Mark the distance on the wallboard. Do the same with the plywood as well. 

Finally, draw two lines on the cutout. Make those lines vertical so that you can work accurately. 

Step 3: Screw the Boards in Place

From this step, we will start working on the exterior of the house. Place the plywood in the opening. Drive two nails on two opposite sides of the board.

Make sure your nails are positioned on the vertical lines you drew earlier. This will ensure a secure placement of the cutout to framing. 

Now. again you will have inside of the house. 

Step 4: Cover the Gaps

Use expanding foams to cover all the gaps between the plywood cut-out and the sheathing. Spray the expanding foam where the plywood cutout met the slathering. This will join them together. 

If you’re thinking about which expanding foam to use for your house, try my recommendations:


These are some of the really good expanding foams. They sit quicker than other foams and are perfect for covering large gaps as well.

Step 5 : Install Insulation

Now you will need to install insulation. Measure the pieces of insulation and cut them into appropriate sizes for fitting. The process is relatively similar to the exposed beam ceiling insulation

After putting in the insulation, set the wallboard in the opening. Again, drive two screws along the vertical lines. 

This will secure the wallboard. 

And voila! Your opening has been filled. Just relax and keep enjoying the newly upgraded AC without worrying. 

At times, you might not be comfortable doing the process by yourself. In such a situation, you better call a professional.

Tips While Filling the Opening 

Tip 1: Use Protective Gears While Using Expanding Foam 

Expanding foams can be really toxic while spraying. Make sure to use protective gloves and masks at all times. Otherwise, it can bring some severe health hazards. 

Tip 2: Use Small Nails for the Plywood 

Plywoods are not too heavy. Using larger screws might extend from the other side of the plywood. Try to use smaller ones. This can get more troublesome with decaying plywoods below sidings.

You do not want to face an accident from the screws. Use drywall screws for better results. 

Tip 3: Use Fiberglass Insulation 

While installing the insulation, try to use fiberglass insulation. Also, ensure that your fiberglass insulation has an R-factor of 13 in it. That is the right kind of insulation to be used in houses. 

Here are some of the tips that can make your task much easier. Do keep them in mind while filling your openings. Also, be cautious so that you don’t hurt yourself. 


Questions: Can an air conditioner be stored on their sides?

Answers: An air conditioner should always be stored in an upright position. The compressor might get damaged if it is stored on the back or sides. This will lead to an expensive repair cost of the compressor. 

Question: Does a through-the-wall air conditioner need a sleeve? 

Answer: Through-the-wall air conditioner needs a sleeve while installing. The wall is not strong enough to handle the weight by itself. So, without the sleeves your wall will not be able to withstand the weight.

Question: How do I fill the space above my window air conditioner?

Answer: If your air conditioner has a casement window then you might find it hard. This problem can be solved by sealing the space. An efficient method of sealing the space is to use an acrylic sheet or plexiglass. 


Here is all you need to know about how to fill an opening from a wall AC. 

Now you can fill the opening in your wall from a wall AC on your own. Contact a professional if you’re not confident enough to do it by yourself. 

Have a beautiful day!