How Do You Weatherstrip a Window Air Conditioner?

ir conditioner weatherseal blog picture 1 from daoseal

It’s great to have a window AC unit to help you beat the heat of summer. What’s not so great? Finding out it is a way for warmed air to escape from your home in winter. It is also a way for cold air to sneak in!

Air conditioner weather seal can solve the problem. In this article, we’ll show you some easy steps for putting weather seal around a window air conditioner. Let’s kick things off with a look at what air conditioner weather seal is and how it works. Read on!

What Is Air Conditioner Weather Seal Like?

AC weather seal is a kind of cellular solid insulating foam. It has a wide range of uses thanks to its chemical and physical properties.


It is sometimes called air conditioner insulating seal. Another common name is air conditioner foam seal.

How is it sold?

It is most often sold in a roll. These come in different thicknesses and widths. You can reel out and cut off the desired length with a pair of scissors. The tape may or may not be self-adhesive. For those with an adhesive on one side, you peel off the paper backing and press the tape in place.


Foam tape is flexible and has a cushioning quality. It is also water-resistant. It may even be waterproof, depending on whether it is closed-cell foam or open-cell foam. It will also tolerate exposure to sunlight and common solvents. Foam tape works in a wide range of temperatures, too.

Of course, the quality of any air conditioner foam seal depends on the manufacturer. Daoseal’s air conditioner weather seal is both waterproof and windproof. Plus, it has “excellent ageing resistance.”


This kind of foam seal is good for dealing with gaps around air conditioners. It comes in handy for various other weatherstripping jobs, too. It weatherizes door and window frames, stopping drafts. It is also quite effective as a barrier to dust, bugs, and moisture

How to Install Air Conditioner Weather Seal

It doesn’t take a lot of time or effort to weather seal an air conditioner with foam tape. The steps will differ depending on whether the unit is already in place.

Scenario One: Before the unit is installed

The most effective method of weatherstripping a window air conditioner is outlined below. You will need measuring tape and a pair of scissors.

Step 1: Clean the surface

This is actually the first step regardless of the approach you take. Start with the surface free of dirt, grease, and grime. This ensures that the adhesive of the weather seal sticks more securely.

Open the window and clean the frame with soapy water. Rinse with clean water and allow to dry completely before continuing.

Step 2: Measure the underside of the window

Open the window and measure across its underside.

Step 3: Cut the required length

Cut the air conditioner weather seal with the scissors. You could also use a utility knife. Rest the tape on a block of wood (or something similar). This prevents damage to the floor or table underneath.

Step 4: Apply the tape

Remove the backing from the tape. Press the tape into the gap with the sticky side up against the underside of the window bottom. Start at one end and press firmly as you go along. Avoid leaving any bumps in the tape.

Step 5: Repeat for the window sill

Measure along the window sill. Cut and peel the air conditioner foam seal. Position the seal with the sticky side down against the window sill. Press firmly in place, again starting at one end and slowly working your way across.

It is worth pointing out that the weight of the unit holds it firmly against the window sill. This makes gaps unlikely under the unit but you should still seal it for good measure.

Step 6: Repeat for the sides of the unit

Measure along either side of the window frame. Cut and peel the air conditioner weather seal, one length at a time. position the first length with its sticky side against the window frame. Carefully press into place as you did at the top and bottom of the unit.

Repeat the process on the other side of the air conditioner.

Air conditioner side panel AC-09D

Step 7: Install the AC unit along with accordion side panel

Set the air conditioner in place. If it has its own accordion side panels, pull them out so that they touch the window frame on either side. Otherwise, cut your own window air conditioner side panels and fit them snugly in place at the sides of the unit.

Daoseal’s version is shown here.

Step 8: Check the fit

Check all around the unit to see if there are any bumps or gaps. Fix any that you find as these will let cold drafts in and warm air out.

Step 9: Seal the top of the window

Measure along the top of the opened window. There is a gap here between the two panes of the window. Cut a length of weather seal and secure it in place here to stop air from entering and leaving.

Scenario Two: The unit is already installed

There are times when the unit is already in place and the entire perimeter has gaps. Some homeowners use a single, long piece of air conditioner weather seal to go right around it. This works to some extent. But, it is better to measure and cut individual pieces for the top, bottom, and sides. For small gaps in a few places, you can cut a short strip of foam tape to fit over each one.

Deciding Whether to Seal and Cover Your AC Unit or Remove It Altogether

High winter heating bills are no joke. A home energy audit could reveal some of the ways in which your home is losing heat and costing you money. Two ways of making sure your window air conditioner is not one of your heat loss culprits are:

  • Sealing and covering the unit
  • Removing the unit altogether

Let’s take a look at both options.

Sealing and covering the window AC unit

Air conditioner weather seal takes care of the openings around the unit. But, what about air passing through the ducts and vents of the unit itself? There are indoor air conditioner covers homeowners can use for this problem. The outdoor air conditioner cover you use to protect the unit during winter can also help to stop drafts.

The foam seal and covers allow you to leave the unit in place for the duration of winter. Once winter is over, remove the covers and inspect the unit. If nothing is amiss, turn on the unit to check that it is still in good working order.

Removing the window AC unit

Some homeowners opt for removing their window AC in the winter. While this is not difficult to do in most cases, there is the risk of damaging the unit. The upside is that after the unit is out, the window can close fully against all the winter weather. You could even now use a window insulation kit to weatherize the window against heat loss.

After removing the air conditioner, give careful thought to how to store it for a few months. You will need to protect it from rodents and bugs that may find it is a cozy winter home! Also, keep it away from moisture and excess heat.

Once summer comes around again, inspect the unit for any signs of damage. Replace it in the window and seal off any gaps. Turn on the unit to test that it is still in good working order.

Bottom Line: Is Air Conditioner Weather Seal a Good Choice?

A window air conditioner is often a source of heat loss during winter. Gaps around the unit can let heated air out and cold drafts in. Air conditioner weather seal is a cost-effective, easy DIY way to stop this. It works, especially when coupled with the use of covers for the unit.

air-conditioner-weatherseal-blog-picture-2 from daoseal
Image by Jill Wellington from Pixabay

Go ahead and enjoy the warmth of your home in winter. Do so without the worry of higher energy bills due to unnecessary heat loss. Take a look at your options for air conditioner weather seal. Make weatherizing your AC unit a priority.