How to Insulate Around a Window Air Conditioner

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Updated August 18, 2022

If you are new to the world of window-based AC units, you may wonder how to insulate around a window air conditioner. The best air conditioners, after all, are only as good as their insulation. So why insulate and what are the varied ways to do it? Keep reading to find out.


  • Insulating around a window air conditioner and window frame is important to maintain efficiency and save on energy bills.
  • You can purchase and install foam side panels or flexible foam insulation material for the air conditioner unit, cutting them down to size if necessary to reduce air leaks.
  • Other insulation options include spray insulation foam for an easy-to-install foam seal and even caulk, using a standard caulking gun.

Why Insulate Around Window Units?

Once you’ve learned how to install window air conditioning brackets, you should start thinking about insulation. A properly insulated window air conditioning unit not only helps maintain a reliable temperature in the room it is placed in but also helps cut down on energy consumption by improving energy efficiency, as you’ll be using the unit less.

Insider Tip

Before settling on an insulation product, go around the exterior and interior of your window to look for any obvious cracks.

How to Insulate Around a Window AC

Luckily, maintaining a window AC unit is easier than learning how to install a central A/C and how to maintain a central air conditioner, and insulation is no different. Plus, it can help make your window A/C colder. You should first identify where the cracks and openings are around the window air conditioning unit, which you can do by holding a candle lighter around the edges to see where there’s a draft that’s moving the flame. To that end, there are a variety of ways to properly insulate your AC, ranging in cost, difficulty level, and general efficacy. Here are a few ideas.

STEP 1Use Foam Insulating Panels

Your first step is to purchase and install foam insulating panels, which are relatively budget-friendly and available at both hardware stores and popular online marketplaces. These panels typically come in large sheets, so you just cut them down to size and then arrange them around your window unit. Be sure to measure the overall dimensions of both your window AC and the window itself before cutting into these foam panels. Some panels come in precut dimensions, so measure before even making a purchase.

STEP 2Use Spray Foam

If you only need to fill minor cracks to fill in some space, choose spray foam. Many of these spray foam products are designed specifically for this task, but you should still work slowly and carefully so as to avoid spilling the foam in unwanted areas. Spray foams sets in almost immediately and can be very difficult to remove. Also, wear protective gloves and eyewear and always follow the manufacturer’s instructions.

STEP 3Use Caulk

Besides newspapers and cardboard, another cheap option is to fill up gaps using standard caulk and a caulk gun. This stuff works best outdoors, however, so you may want to think about a combination of caulk and spray foam to cover your indoor and outdoor needs. As with the spray foam, work slowly and carefully while operating the caulk gun.


How to install window air conditioner insulating panels?

They are fairly easy to install, just cut and place, though you may need to try a few times to get a perfect fit or seal.

How to get more from your window air conditioner?

Remove the window sash during use and remove the entire unit during the winter months, so as to eliminate any cold air from seeping in under the high-density foam seal.

How much can an air conditioner cool?

Window unit air conditioners cool a great deal, but this depends on each design and its compressor, motor, and fans. Read the stats for more information.

STAT: If you fail to insulate the window air conditioner, the warm air in your room will leak around the unit’s perimeter. Also, precipitation from the outside will get indoors and reduce the AC’s efficiency. (source)

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