You’ve got a portable air conditioner, or you’re about to buy one, and your only window slides sideways. The little kit in the box was probably made for a standard up-and-down window, so now you’re staring at a wide gap and wondering how to close it. So how do you install a portable air conditioner in a sliding window?
In short: measure the opening, fit the vent panel into it, fill any leftover space with foam or rigid board, seal every gap, and lock the window. Get the seal right and the unit cools your room instead of leaking hot air back in.
Why the window setup matters so much
A portable air conditioner pulls heat out of your room and pushes it outside through an exhaust hose. If that hose isn’t vented properly, or hot air sneaks back in around it, the unit has to work harder and your room stays warm. Think of the window panel as half the system, not a minor accessory.
What you’ll need
- The air conditioner with its exhaust hose and hose adapter
- The window kit that came with it, or a sliding window kit made for the purpose
- A tape measure
- Weatherstripping foam or adhesive-backed foam tape
- Scissors or a utility knife
- Painter’s tape or duct tape for temporary sealing
- A piece of wood or plexiglass, only if your kit doesn’t fit your window
Measure the opening first
Open the sliding window to the width you want and measure the opening in inches, both height and width. Then compare those numbers to the adjustable panel size in your kit instructions.
Many kits stretch to cover a typical range, but sliding windows can be much taller than the panel, especially patio-style doors. If the gap is bigger than the panel, you’ll fill the rest with a foam block or a piece of rigid board cut to fit.
Find the right spot for the unit
Set the air conditioner on a level, hard floor near the window and close to a grounded outlet. Skip extension cords and power strips, because these units draw a lot of power, and the manual will usually tell you to plug straight into the wall. Leave some clearance around it so air can flow in. Most manuals suggest a foot or so from walls and furniture.
Connect the hose and adjust the panel
Attach the exhaust hose to the back of the unit and the other end to the window adapter. Extend the hose only as far as you need, since shorter is better. A long, stretched or sagging hose loses cooling and sheds heat into the room, and sharp bends choke the airflow, so keep it as straight as you can.
Then adjust the window panel to the width of your opening. Most kits have two or more sections that slide to fit.
How to fit the panel in a sliding window
Because the window slides horizontally, the panel usually stands upright in the gap, with the slider closing against its edge. Here’s the order that works for most setups:
- Open the window to the width of the panel.
- Insert the panel into the opening and push it into the track.
- Slide the window closed against the panel until it’s snug.
- If the panel is shorter than the window, fill the leftover space at the top with rigid board or foam so there are no open gaps.
- Connect the hose adapter to the panel opening.
If the panel doesn’t sit firmly in the track, add a spacer block under it so it can’t wobble or slip out.
Seal every gap
Here’s the step people skip and then regret. Use foam seal strips to close gaps along the edges of the panel, between the panel and the window frame, and where the sash meets the glass. Press firmly so the foam compresses.
Then check for light or a draft. If you can feel hot air or see daylight, keep sealing. A tight seal can make a visible difference in how fast the room cools.
Keep the window secure
A sliding window propped open by a panel can be a security risk. Many people add a track lock or a wooden dowel in the track so nobody can push the window open from outside, which is worth doing on a ground floor. Make sure the whole setup can’t tip or fall out of the window too, especially above ground level.
What about the water it collects?
Some portable units evaporate the moisture they collect and send it out through the hose. Others gather water in a tank or have a drain port, particularly in humid weather. Check your manual to see which you’ve got. If there’s a drain, position it over a floor drain or attach a hose as instructed, and empty the tank when the unit signals it’s full.
Tips for better cooling
- Close the door and the room’s curtains or blinds to block sun.
- Size the unit to the room. The manual or label usually lists a recommended room size, and sunny rooms or kitchens need more capacity than the minimum.
- Clean the filter regularly, often every couple of weeks in heavy use.
- Keep the hose out of the sun and away from furniture.
- If you can, pick a two-hose design. A single-hose unit pushes room air outside, which can draw warm air in through other gaps, while a two-hose unit uses outside air to cool itself.
Frequently asked questions
Can you use a portable air conditioner without a window?
Not well. The exhaust hose has to send hot air outdoors, and venting it into another room just moves the heat around. A sealed window panel is the standard way to do it.
Why is my portable AC not cooling after I installed it?
Leaks are the usual suspect, so look for gaps around the panel and a hose that’s long, bent or sagging. An undersized unit or a sunny room can also hold it back.
Is it safe to leave a sliding window open with an AC panel?
It can be a security issue, so add a track lock or a wooden dowel in the track. Also make sure nothing can tip or fall out, especially above ground level.
The bottom line
Once you’ve nailed how to install a portable air conditioner in a sliding window, a fan can help spread the cool air around. Our roundups of the best quiet bedroom fans with remote and the best ceiling fans with lights for bedrooms cover circulation. Still shopping for the unit itself? Compare models in our guide to the best portable air conditioners for sliding windows. And if the heat’s keeping you up at night, you might like our tips on making your bed cooler.