What is a window seal for?
Short answer: without a seal, the window gap where the hose comes out lets hot outside air flow straight back into the room — your portable AC works against itself, cools less and uses more electricity. A custom acrylic plate closes that gap completely: hot air leaves through the hose and doesn't come back in. It's the difference between a portable unit that "just about copes" and one that genuinely cools the room.
Custom acrylic plate vs. fabric kit
There are two types of seal on the market. The zip-up fabric kit is cheap and universal, but fits poorly on casement windows and old frames — exactly the most common kind in Lisbon's buildings. The rigid acrylic plate is made to the millimetre for your window.
| Criterion | Fabric kit (zipper) | Custom acrylic plate |
|---|---|---|
| Sealing | Okay; leaves gaps on casement windows | Total — cut to the millimetre |
| Old Lisbon frames | Hard to fit | Fits any window |
| Durability | Fabric wears out after one season | 4 mm acrylic, lasts years |
| Light / privacy | Blocks the light | Clear (lets light in) or opaque for the bedroom |
| Looks | Improvised | Clean, discreet — great for short-term rentals |
| Price | €10–30 | From €49, made to measure and delivered |
Custom-cut acrylic window seal plate
- Works with any portable air conditioner you already own — we just need the window and hose measurements
- 4 mm acrylic cut to the exact width and height of your window
- Hole for the hose (sized to your hose, usually 13–15 cm)
- Choice of fixing: velcro (no drilling) or thumb screws
- Opaque version (white or black) +€10 — blocks the light, ideal for bedrooms and short-term rentals
- We ship across Portugal (Lisbon delivered; rest of the country via CTT) — we confirm your measurements before cutting, no mistakes, no returns
How to measure (30 seconds)
To make the right plate we need three measurements. Take them with a tape measure and send them over on WhatsApp:
| Measurement | How to take it |
|---|---|
| Opening width | Side to side of the gap where the plate will fit (cm) |
| Opening height | Top to bottom of the same gap (cm) |
| Hose diameter | Measure the end of the AC hose (usually 13–15 cm) |
Not sure? Send a photo of the window on WhatsApp and we'll help you measure. We confirm everything with you before cutting.
How it installs
The plate sits in the window opening during the warm months. With velcro it sticks to the frame without drilling (ideal for rented flats); with thumb screws it sits even more firmly. The hose slots into the hole and stays put. At the end of summer you take it out and store it — no works, no marks, no landlord permission needed.
AC Rental Lisbon's note
We see it in hundreds of Lisbon flats: the portable unit is good, but the hose hangs out of a half-open window and half the cool air is lost. A made-to-measure plate fixes it for good — and if you rent from us, you can add the plate to your AC delivery.
FAQ
What's the difference between the acrylic plate and the fabric kit?
The fabric kit is universal and cheap, but leaves gaps on casement windows and old frames. The acrylic plate is cut to the exact size of your window, seals completely, lasts years and looks better.
Will it fit my window?
Yes — it's made to measure. It works on sliding, casement and tilt-and-turn windows. Just send the width, the height and the hose diameter.
Do I need to drill the wall or frame?
No. The velcro fixing sticks to the frame without drilling, and the thumb screws don't need any works either. You can remove everything at the end of summer.
Does the plate let light through?
The clear acrylic version lets natural light in. If you'd rather block the light (a bedroom or short-term rental), there's an opaque version in white or black.
How much is it and how soon do I get it?
From €49 for the clear version, with delivery in Lisbon included (opaque +€10). We confirm your measurements and arrange delivery over WhatsApp.
I already own a portable air conditioner. Will the plate work?
Yes. The plate is made to the measure of your window and hose, so it works with any portable air conditioner you already own — it doesn't have to be rented from us.
Do you deliver outside Lisbon?
Yes. In Lisbon and Greater Lisbon we deliver directly; for the rest of Portugal we ship via CTT (shipping confirmed on WhatsApp). As it's made to measure, we confirm everything before producing.