How to install window air conditioner in a new home without the outer sill

To install an air conditioner window, a secure hanger is needed to configure the unit. For most of the windows, an outer ledge and the window frame provides a sufficiently large hook for this purpose. However, if you do not have a threshold, you can still install the air conditioner. All you have to do is add a mounting bracket on the outside of the window. The bracket on the same level as the base of the window frame provides the necessary mounting platform. The base of the window frame the same amount of space that you would an external threshold extends, allowing you to place your air conditioning in the frame without fear of it falling due to lack of proper support.

You will need

  • Mounting bracket for air conditioning
  • Screwdriver
  • Wood screws or sheet metal
  • Window Air Conditioner
  • Extensions for air conditioning
  • Putty
  • Foam weather-stripping


Unit placement

  1. Measure the window opening height and width using a tape measure to determine the maximum size unit air conditioner that can be installed in the space available. Buy one small enough to fit on the opening drive.
  2. Lift the sheet bottom window completely. Locate the center point of the window and mounting bracket positions the unit for air conditioning so that the mounting holes overlap the outer edge of the window frame, with the lip at the top of the bracket upward and level with the plane of the window in which the blade rests when the window is closed. Check the level with a carpenter’s level before assembly.
  3. Set the mounting bracket in place with sheet metal screws through the mounting holes and the window frame. For vinyl and wood frames, use wood screws. To support the weight of the unit air conditioning, mounting bracket serves as an alternative to the outboard end of the windowsill.
  4. Lower the leg of the stand that rests outside the window so that it is in the farthest corner from the bracket to the wall below the window edge. Screw the leg of the stand to the wall to help keep the bracket under the weight of the unit air conditioning.
  5. Lift the unit air conditioner in the window. Have an assistant ready outside, if possible, to help you position the unit. Center the unit in the window so that the mounting bracket is also centered. Push the unit through the mounting bracket. A small catch in the bottom of the unit assures the mounting bracket while sliding along the unit by clicking in place when the unit is in the correct position.
  6. Close the window until it rests on top of the unit air conditioning.

Add Windowing Extensions

  1. Pull the extensions window on each side of the unit air conditioning to the outside of the unit, until they touch the sides of the window frame. Extensions must be stretched into place like an accordion.
  2. Ensures extensions on the sides of the window frames by placing screws through the mounting holes on the sides of the extent and under. Using the same screws used for mounting support.
  3. Extensions ensure sash installing screws through the mounting holes along the top of the extension, in the front of the blade.

Finishing Touches

  1. Place a bead of caulk around the edges of the unit air conditioning, then smooth the caulk with a wet finger.
  2. Fill any open along the top of the bottom sheet of the open window between it and the blade of the upper window with weather-stripping to help isolate space.
  3. Plug unit air conditioner to a nearby outlet and follow the manufacturer’s instructions for use in the cooling of your room.