Portable AC window kit leaking or letting in outside air

Symptoms

• Draft or outside air felt near the window
• Rain or moisture coming in around the panel
• Reduced cooling efficiency
• Daylight visible through gaps in the kit

Likely causes

• CommonFoam seal strips missing, worn, or not appliedThe foam strips that come with the kit seal the gaps between the panel and window frame.
• CommonWindow kit panel not sized correctly for the windowAdjustable panels need to be extended fully to the window's width and locked in place.
• PossibleWindow not latched or locked down onto the panelAn unlatched window can shift and open a gap over time.
• PossiblePanel installed in a sliding or casement window without the right adapterStandard kits are built for double-hung windows and need extra parts for other window types.

What to do

1. Apply or replace the foam weatherstripping strips along all edges where the panel meets the window frame and sash.
2. Extend the adjustable panel fully so it fits snugly with no visible gaps, then lock or screw it in place if the kit allows it.
3. Close the window down firmly onto the top of the panel and latch it if possible to prevent shifting.
4. Check for daylight or drafts by running a hand along the edges with the AC off.
5. If the window is a slider or casement type, look for a kit adapter designed for that window style.
6. Add clear tape or removable weatherproof caulk along stubborn small gaps for an extra seal.

Tools and parts

• Scissors
• Weatherstripping foam
• Clear tape (optional)

When to call a pro

This is a DIY task; a handyman can help if the window type needs a custom-built panel that the standard kit doesn't fit.

Safety