How to Fill Gap in Window Air Conditioner | A Step by Step Guide


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Window Air Conditioners are great to keep the room cool and pleasant during the hot summers. However, all the ACs don’t fit the windows exactly. Sometimes a gap is left behind that causes different issues. Filling the gaps between the window frame and AC is necessary as if left unchecked; it will decrease the efficiency of the room cooler. Also, this may let dust and bugs enter the room. So, filling such gaps is necessary to maintain the efficiency of your AC. Let’s learn how to fill gap in window air conditioner.

Many effective methods can be used for such a purpose. However, some are too difficult to adopt. In the later section of this short guide, we’ll discuss some effective methods for such a task.

How to Fill Gap in Window Air Conditioner

How to Fill Gap in Window Air Conditioner

What is required? 

Here are the materials required to fill the window frame and AC gaps. 

  • Measuring tape
  • A cutter 
  • Weather-stripping
  • Cloth
  • Rope caulk
  • Vacuum cleaner 

Filling the Large Gaps

Though larger gaps between the window frame and AC are harder to fill, here is an easy method to do this task. Gaps larger than ⅛ inches can be filled with such a method. 

You’ll have to fix the weather-stripping, so cleaning the surrounding surfaces of the window and AC is necessary. 

  • Clean the surrounding areas of the AC and window with the help of a vacuum cleaner. 
  • You can also use a cloth to clean the greasy and adhesive material if any. 
  • Measure the length of the gap. 
  • Cut the equal weather-stripping that fits the size. 
  • Peel off the back of the weather-stripping. 
  • Put it on the underside of the window. 
  • Press the weather-stripping alongside the whole window on one side while the AC is on the other side to get it fixed to the gap. 
  • Ensure that the foam is on the gap side, as this will help in the airtight closure of the gap. 
  • You’ve done with the window AC gap. 

Filling the Narrow Gaps

  • Rope caulk is a good choice to close the window AC gaps that are less than or equal to ⅛ inches in thickness. Here is how to do this. 
  • In the same manner, start by cleaning the surrounding surfaces. 
  • Measure the space between the window frame and AC. 
  • Cut the equal-sized rope caulk. 
  • Push the caulk into the gap. 
  • If you feel that the rope is not fitting the gap well, you may push two pieces. 
  • After you’ve closed the gap tightly, smooth the surface of the caulk and remove the debris with the help of a vacuum cleaner. 
  • You’ve done with the smaller window AC gap. 


Closing the gap between a window AC and the window frame is necessary as it has a bad impact on the performance of the AC. Moreover, such a gap can greatly disturb you as it will let the hot air pass that will warm up the room.

Furthermore, it’s an entrance to the light, dirt, and even bugs that will affect you. You can choose any of the methods mentioned above to do this effectively as per the gap size! 

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