How to vent a portable AC through a sliding window
Horizontal sliders are what most universal AC kits are designed for. Fit the panel vertically, slide the pane onto it, and close the small side gap.
A horizontal sliding window is a sash window turned on its side. The pane slides left to right, leaving a tall opening you fill with a vertical panel. Nearly every universal portable-AC kit is shaped for this geometry, so it is among the cheapest and quickest types to vent.
The method
Slide the pane open, stand the adjustable panel vertically in the opening, and slide the pane back onto it. The panel adjusts to your window height and carries the hose flange. The same kits sold for sash windows work here, often the least expensive option in the range.
For odd sizes, a custom acrylic panel cut to height gives a tighter fit. A dual-hose unit needs a taller panel or two holes.
Close the side gap
Where the moving pane meets the fixed pane there is usually a small vertical gap. Foam strip closes it. It is the slider equivalent of the sash meeting rail: easy to miss, and worth a minute to seal.
Security and rain
Add a track stop or a cut length of dowel in the slider track so the pane cannot be forced open from outside while the panel is in place. Slope the hose down to the outside so rain sheds away from the panel.
Single hose, dual hose or split
Because the panel seals the opening cleanly, a single-hose unit performs well on a slider. Dual-hose and split units add headroom for bigger or sunnier rooms. The right class depends more on the room than the window.
Use the finder to size the unit to your room, then come back for the seal that fits.
Get a unit matched to your room
The finder turns your room, window and budget into a short list, ordered best match first.