How to vent a portable AC through a casement window

A casement window is side-hinged and swings open like a door. Two versions exist across Europe, and they call for different solutions. Inward-opening casements behave like a tilt-and-turn window in its turn position. Outward-opening casements, common in the UK, Ireland and France, are the harder case.

Inward-opening casement

Because the sash swings into the room, there is no sash-in-track gap to seal and no point running a hose through the window while it stands open. Instead, mount a seal across the whole frame and then close the window onto it.

A full-frame cloth kit such as the Trotec AirLock 100 is the simplest route: fit it with the sash open, feed the hose through the zip, then bring the sash back to rest against the cloth. For a dual-hose unit, the AirLock 200 gives you the second opening.

Outward-opening casement

Here the glass is gone from the frame when the window is open, so the seal has to fill the entire opening. Off-the-shelf slot kits, the kind built for sash and sliding windows, do not fit. You have two realistic options.

Custom rigid panel. A pane of acrylic or PMMA cut to the exact opening, with a 150 mm hole for the hose, fixed with removable tape or hook-and-loop. German acrylic shops cut these to measure for around the cost of the material; many AC owners use 6 mm acrylic. It is the neatest, most secure result and the one most outward-casement owners settle on.

Cloth kit for tilting and casement windows. Some fabric kits are sold specifically for casement openings and zip closed around the hose. Cheaper than custom acrylic, less rigid, and less secure, so better for a short season than a permanent setup.

A budget version is a panel of foam board or twin-wall polypropylene cut to the opening and hole-sawed for the hose. It works, but weatherproof the edges or rain finds its way in at the perimeter.

Weather and security

An outward casement physically cannot close over a fat hose, so the panel stays in the opening while the unit runs. That makes two things matter:

• Weatherstrip the panel edges so rain does not run in around them, and slope the hose down to the outside.
• Make the panel rigid and snug. A loose panel an intruder can push out is a weak point on an accessible floor. On a ground or first floor, prefer a tightly fixed rigid panel over a propped-in one.

If your building allows something outside the window, a mobile split avoids the panel entirely; only a thin line crosses the opening, and the window can close behind it.

Single hose, dual hose or split

A single-hose unit relies on a good seal to avoid drawing warm air back in. A dual-hose unit needs two holes in the panel. A mobile split needs only a small penetration for its line, which suits an awkward outward casement well.

Use the finder to see which class fits your room, and it will point you to the right seal for the window you choose.