Window Air Conditioner Insulation

Window air conditioners are a boon on hot summer days and nights. But they let in cold air during winter. Sometimes a lot of cold air. Eliminating drafts is usually a simple inexpensive DIY project.

Window Air Conditioner Insulation

Remove the Air Conditioner

The best way to eliminate air leaks is to remove the unit completely and close the window. This is not always practical. They are heavy, hard to handle, and want to fall onto the ground when the fasteners are removed.

If you take yours out, make sure you clean it, dry it, and store it safely. It has to be reinstalled next year–and still work.

Seal the Air Leaks

Air leaks around window air conditioners can be responsible for up to 25% of cold air in a room. Some gaps around the unit are easy to see–letting air–and insects–pass through unhindered. Smaller gaps may require a smoking candle or a lighter to find. Move the candle or lighter slowly around the air conditioner close to the window. Smoke from the candle will flow with the air. Flame will flicker in a draft.

You can then use one or more methods to seal the gaps.

  • Compressible Foam. Available in strips or can be cut from larger sheets. Usually compressed between the window sash and the air conditioner and/or the unit and sill.
  • Foam Tape. Peel and stick backing. Install around the perimeter of the air conditioner where it meets the window, sill, and accordion side pieces.
  • Spray Foam. Easily fills gaps up to ½”. Can be messy and difficult to remove. Only use low-expansion foam.
  • Caulking. Easily fills gaps and cracks up to ¼”. Very effective. Waterproof. Difficult to remove.

In actuality, warm air always moves to cooler areas. On still days, you are losing heat to the outside. Wind changes that dynamic and will blow air into the house.

Store-Bought Insulation Covers

Premade insulated covers are available online, from home improvement outlets, and from most stores selling air conditioners. They are made for both interior and exterior applications in multiple sizes. All of them should have integrated fastening systems. Many of them cost less than $20.00.

Exterior covers provide superior protection. They protect the air conditioner’s housing and interior from the elements and wind pushes them onto the machine. They may be difficult or impossible to install–such as on units in apartment windows or the second story of a house.

Interior insulation covers fit over the inside of the unit. For extra protection against wind and water penetration, remove the cover and wrap the interior components with plastic. (A garbage bag or two should be sufficient. Tuck the excess plastic into the cabinet and replace the cover. Then install the insulated blanket.

Foam kits that fit inside the air conditioner are also available in various sizes. They usually come with self-adhesive strips which may or may not withstand weather conditions.

DIY Insulation Covers

Remove the cover from the conditioner housing. Fill the open areas with plastic to stop wind and water. Replace the cover. Buy half-inch to one-inch thick soft foam, cut it to size, and wrap the air conditioner housing. It can be kept in place with duct tape or packing tape.

The pleated side pieces of air conditioners are very thin and let warm air escape. Cut and fit foam over them at the same time. The foam can be taped to the window sash, sill, window frame, and air conditioner.

Anyone with a sewing machine and a little talent can make a cover from a padded moving blanket. Sewing elastic around the open end makes for a snug fit and quick and easy installation and removal. Any thick padded material that resists wind and moisture will work as well.