How to Muffle a Noisy Window Air Conditioner

Window air conditioners are a low cost way to make your home comfortable, allowing cooling only the rooms in use. They are much less expensive to buy than having central air installed. One problem with them is that they tend to be noisy. This project shows a way to reduce the noise.


  1. Image titled Lower ac muffler box empty
    Construct a box using sheet rock (dry wall). Two by two inch lumber works well for the corners. Use a utility knife to cut the sheet rock to size, scoring one side and then breaking it along the score. Dry wall screws hold the sheet rock to the wood. The back of the box and the bottom side are left open. Size the box so that it covers a bit more than the width of the air conditioner and so that the opening at the bottom has as much area as the inlet area of the unit to avoid reducing efficiency. If you plan to add sound deadening padding to the inside, add additional size to the box to keep the airflow up. The box should be tall enough to go from just above the inlet of the unit to several inches below the bottom edge of the unit.
  2. Image titled Ac muffler lower with mattress pad
    Optionally add pieces of foam mattress topper to the inside of the box to absorb sound.
  3. Image titled Ac muffler mounting blocks
    Screw pieces of 2x2 to the wall next to the air conditioner for mounting the box. Trim the edges of the box to fit tightly around the air conditioner and screw it to the mounting blocks so that the top of the box is just above the inlet to the unit, but below the outlet.
  4. Image titled Ac muffler upper with mattress pad
    Build another box, open at the top and bottom and on the back. Size it to cover the outlet portion of the unit, but to leave the controls exposed. Optionally, add mattress padding for sound deadening, but keeping the open area in the box at least as large as the outlet area to keep efficiency up. This box will rest on top of the lower box and extends several inches above the air conditioner.Trim the sides of the box to fit snugly against the air conditioner.
  5. Image titled Ac muffler completed1
    Attach additional blocks to the wall as needed for mounting and screw the upper box to the mounting blocks.


  • You will probably want to do some finish work to the outside of the box to improve appearance.

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Categories: Doors and Windows