The window sealing kit is the unsung hero of mobile-AC cooling. It's a simple accessory, but without it your expensive air conditioner barely works — and with it, you get full cooling with no drilling. Here's everything renters need to know.
What a window sealing kit does
A mobile AC vents hot air outside through an exhaust hose, and that hose has to go through an opening — usually a window. The problem: an open window around a hose lets the hot air you just pushed out flow straight back in, so the room never cools. A window sealing kit solves this by fitting the window opening, letting the hose pass through, and sealing the rest of the gap. It's the piece that turns "hose out the window" into actual cooling.
Why it's not optional
This is the single most common reason people think a mobile AC "doesn't cool": they run the hose out of a cracked window without sealing it, and the heat cycles back in. The unit is fine — the setup isn't. Fitting a sealing kit typically transforms the cooling. So treat the kit as essential equipment, not an optional extra (see our exhaust hose mistakes guide).
Types of sealing kit
There are two main styles:
- Fabric kits — a zippered cloth panel that fits the window frame and seals around the hose. Flexible, work well with tilt-and-turn windows, easy to fit and remove. The renter favourite.
- Rigid panel kits — adjustable solid panels, more common for sliding-sash windows, less suited to typical German windows.
For most German flats, a fabric kit is the practical choice.
Fitting German tilt-and-turn windows
Germany's common tilt-and-turn windows don't suit the rigid, sliding-window kits sold in some markets — but fabric kits are designed for exactly this. They seal around the opening when the window is tilted, letting the hose exit while blocking the gap. Crucially, they install with no drilling and remove without a trace, which is what keeps a mobile AC renter-friendly. See our no-drill cooling guide.
Renter-friendly by design
A fabric window kit ticks every renter box: no tools, no holes, no permission needed, and fully removable when you move. It's the accessory that lets you enjoy full mobile-AC cooling without touching the building or risking your deposit. Pair it with the unit and you have complete, reversible cooling.
Fitting tips
- Size it to your window — kits come in sizes or adjust to fit; check yours.
- Seal fully — close any leftover gaps so no warm air sneaks back.
- Keep the hose short and straight from unit to window for best airflow.
- Remove and store it with the unit at season's end.
The takeaway
A window sealing kit closes the gap around a mobile AC's hose so the cooling actually works, and a fabric kit fits German tilt-and-turn windows with no drilling — keeping the whole setup renter-friendly. It's essential, not optional. When you buy a mobile AC, make sure you have a kit; check which units are in stock near you.