Window Too Wide for Air Conditioner? (Here's What You Can Do)

Patricia Oelze
by Patricia Oelze

Air conditioner installations can be tricky for any homeowner. But, when your window is too wide, that can make the process that much harder. Follow along as we explore how you can fill those gaps and install your window AC unit without a hassle.

If you are considering replacing your windows, get a quote from local contractors in your area here.

Air conditioners never seem to just fit perfectly into any window. So, it will not come as a surprise when you go to put your window AC in, and it is too small. How are you supposed to fill those giant gaps?

There are many ways to fill the gaps between your window air conditioner and the window. Most AC units have spacers on the sides that are adjustable to fit many windows. But often you end up having to make a barrier to fill it in from foam, wood, or some other material.

Even if your air conditioner does come with those side accordion-style curtains, sometimes they do not bridge the gap all the way. And those curtains are not very energy efficient anyway. It is better to make your own insulation to fill in these spots.

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Using Foam Board Insulation is a Great Choice

Foam board insulation comes in many different sizes and thicknesses. They have several types as well. Here is a good example of the details of each:

Type of FoamProsCons
Expanded Polystyrene Foam· It is the least expensive

· Similar to foam peanuts

· It is the least efficient

· The R-value is only 3.6 to 4.0 per inch

Extruded Polystyrene Foam· The medium insulation board is most commonly used

· Has an R-value of 4.5 to 5.0 per inch

· Easy to use

· Costs more than the expanded poly

· Not as efficient as the Polyisocyanurate

Polyisocyanurate· The most efficient foam

· Has an R-value of 7.0 to 8.0 per inch

· Foil back makes it easy to tape

· Moisture resistant

· It is the most expensive foam insulation board

· May release HCFC or CFC gasses

Spray Foam Sealant Can Also Work

Since 1986, people have been using this awesome foam to insulate and seal all sorts of projects around their home or at work. It has excellent energy efficiency benefits and expands to fill any opening. Not only is it an insulation, but it is also an air barrier. It never loses its shape and can be used anywhere.

Spray foam is also waterproof, so it protects from leaks and moisture. It does not absorb any water at all. It just repels it, so you do not have to worry about mold or mildew. The foam lasts decades too so you will not have to redo it anytime soon. And with an R-value of about 6.5 to 7.0 per inch, it protects better than most other foams and insulations.

Insulating Side Panels Are a Thing

The hardware store actually sells insulated side panels for use with window air conditioners that do not fit. They can be used with or without the accordion-style wings on your AC unit and they are great for blocking air leaks.

At most hardware stores, you can get panels up to nine inches wide and 18 inches tall. Just cut it to fit and seal it with caulk or weather-stripping tape. Use it over the accordion panels to make it even more energy efficient. They are washable so you can clean them every year or whenever they get too dirty.

Try Some Plywood with Weather Stripping

After placing your AC unit in the window, secure it, and measure the space between the AC and the window frame. Then all you have to do is cut a piece of plywood to fit. Place it in the gap and seal it with caulk, weather stripping, duct tape, or spray foam sealant.

You could also use a mixture of sawdust and wood filler to fill the gaps between the plywood and air conditioner. This can be done by sanding the plywood just enough to get some sawdust. Mix it with the wood filler, put it in a syringe, and squirt it into the gaps. Using the sawdust will make sure it is the right color.

You Can Always Go with the Classic Cardboard Look

Rather than using wood or one of the other insulations, you can just use the classic cardboard fix. Although this is not as energy-efficient, it will do the trick until you can think of something else. Seal it with duct tape, weather stripping, caulk, or spray foam sealant.

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Related Questions

How Can I Stop Burglars from Getting Through a Window Air Conditioner?

Many thieves specifically look for homes with window air conditioners because they are usually easier to break into. All it takes is unhooking the braces on the outside and pushing the air conditioner into the house.Add Sliding Window LocksThese little metal locks just slide onto your sliding track in your window. You tighten it up and it stops anyone from opening your window. Simple, easy, and cheap. Their only drawback is that they take a bit of time to remove in an emergency. But that is okay if you have another window or door to use for an emergency exit.The Security BarThere are several types of these on the market. They are basically just a bar that you place at the top of your window to keep burglars from being able to open it from the outside. They have two different types.

  • The 110 Bar adjusts easily and has an automatic lock when you let go of it. You can also release it easily just by pressing a button. The anti-lift lock is perfect to keep out criminals.
  • The 112 Bar is also adjustable and is childproof as well. You can install it with screws or tape. It is not pressure locked so it does not come loose. Perfect for window air conditioners and is easy to open in an emergency.

Window Alarms

Although a window alarm will not prevent the window from opening, it will usually scare away anyone trying to break in as soon as they hear it. You can get a whole-house system that includes the windows, or they have specific alarms just for windows. And if the noise does not deter the burglar, at least you will know they are coming and can prepare for them or call 911 if you are home.

What About Using a Portable Air Conditioner Instead?

Portable air conditioners are similar to window units in that they both use refrigerant to cool the room. The liquid coolant absorbs the heat from the air as it flows over a set of coils inside the AC. When the refrigerant absorbs the heat, it changes from a liquid to a gas. The compressor then vents this gas out the window or wherever you have it venting to.

While you do not have to put a portable window unit in your window, you will have to vent it through the window or another opening nearby. This is usually done with a hose that reaches up and out the window. They usually come with an easy-to-install kit that only takes a few minutes to hook to your window. You can also move it from one room to another easily.

If you have little or no floor space, a window unit is a better idea though. Although portable air conditioners are not huge, they are typically about 30 to 36 inches tall, 17 to 24 inches wide, and weigh about 50 to 75 pounds.

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Patricia Oelze
Patricia Oelze

I am a DIYer who loves writing about anything home-related. When I am not writing, you can find me studying for my PhD in Psychology, photographing nature, and swimming at the lake with my grandkids.

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