How to install a window air conditioner

• Tape measure
• Cordless drill-driver and bits
• Screwdriver
• Spirit level
• Pencil
• Utility knife (for trimming foam seal)

Before you start, lay everything out on a soft surface (the flattened box works) and check it against the parts list in your manual.

• Air conditioner unit
• Side accordion panels and top rail
• Support bracket or sill brackets (if supplied or required)
• Foam window seal strips
• Sash lock bracket and screws

1. 1

   Step 1: Measure the window opening width and the clear height when open, and compare them with the manual's minimum and maximum; also check for a suitable outlet within reach of the power cord.

2. 2

   Step 2: Clear the sill inside and out, and check that the frame and sill are sound; soft or rotten wood cannot hold the unit and must be repaired first.

3. 3

   Step 3: Fit the support bracket to the outside of the sill exactly as the manual shows, using its screws, and set its angle; some units must have it, others supply sill supports instead.

4. 4

   Step 4: Attach the top rail and slide the accordion side panels onto the unit while it sits on the floor, so they are ready to extend once it is in place.

5. 5

   Step 5: With your helper, lift the unit into the open window so its bottom channel sits over the sill and its weight rests on the bracket, keeping hold of it the whole time.

6. 6

   Step 6: Lower the window sash down behind the top rail so it traps the unit, then check the tilt: most units must lean slightly backward outside so condensation drains away, as the manual specifies.

7. 7

   Step 7: Pull the side panels out to the window frame on both sides and screw them to the sash or frame with the supplied screws.

8. 8

   Step 8: Fit the sash lock bracket so the window cannot be lifted again from inside or out, and press foam seal into the gap between the upper and lower sashes.

9. 9

   Step 9: Seal any remaining gaps around the panels with the supplied foam, trimming it to fit, so warm air and insects do not get in.

10. 10

    Step 10: Plug the unit directly into the wall outlet, switch it on, and check that it cools, that water drips outside rather than indoors, and that nothing rattles.

• Relying on the window sash alone to hold the unit, with no bracket or support under it.
• Mounting it level or tipped inward, so condensation runs into the room.
• Running it from an extension lead or a shared power strip.