You can run it, but it still needs somewhere to exhaust hot air, so a window is not strictly required. People vent the hose through a sliding door, a drop ceiling, a wall opening, or a dryer-style vent instead. Running a portable AC with no exhaust path at all simply moves heat around and will not cool the room.
Why can't a portable air conditioner cool without an exhaust path?
A portable air conditioner removes heat from the room and blows it out as hot exhaust. If that exhaust has nowhere to go, it simply re-enters the same space, and a sealed room slowly gets warmer instead of cooler.
Any opening to the outdoors can work as the exhaust route. What matters is that the heat physically leaves the room, not that it specifically leaves through a window.
Running a portable unit with the hose disconnected, or coiled up inside the room, is the classic mistake. It looks like the unit is working since cold air still blows from the front, but the room actually warms up over time.
Exhaust hose and compressor heat
The exhaust hose carries away both the heat pulled from the room and the extra waste heat the compressor generates while running. Blocking or kinking that hose traps compressor heat inside the unit, which can trigger a safety shutoff.
Where can the exhaust hose vent besides a window kit?
Common alternatives to a window kit include a sliding-door vent panel, a drop-ceiling tile cut for the hose, a hole through an exterior wall, or a dryer-style wall vent. Each gives the hot exhaust a sealed path to outside air.
Whatever the route, keep the hose short and as straight as possible. A long, sagging, or kinked hose lets exhaust heat radiate back into the room and makes the unit work harder for the same result.
Seal the gap around whichever opening you use with foam or tape made for the purpose. An unsealed cut in a wall or ceiling lets warm outdoor air leak straight back in, undoing much of the cooling effort.
Single-hose vs dual-hose venting
A single-hose unit pulls room air for its exhaust, creating negative pressure that draws warm outdoor air back in through any gap. A dual-hose unit draws outdoor air separately for that job, so it holds a room's temperature more efficiently through whichever opening you use.
That difference matters more in a room without a convenient window, since a less airtight vent path — like a gap around a door panel — gives negative pressure more opportunity to pull warm air in on a single-hose model.
Does venting distance affect cooling capacity, CFM, and noise level?
A longer or more indirect vent path slightly reduces effective cooling capacity, since the compressor works harder against the added resistance. CFM airflow through a longer hose run drops a little, and noise level can rise as the unit compensates.
None of this stops the unit from working; it just means a wall vent routed a long way from the unit performs a bit worse than a window kit placed right next to it. Placing the unit as close as possible to whatever opening you use minimizes that penalty.
BTU, square footage, and SEER efficiency
None of these venting choices change a unit's BTU rating or how well it matches your room's square footage. A higher SEER unit will still use less power for the same cooling job, whether it vents through a window or a wall.
Can you still get self-evaporating dehumidifier action without a window?
Yes. A self-evaporating unit's dehumidifier function works the same way regardless of where the exhaust hose vents, since it evaporates collected condensate out through that same hose. Any sealed vent path supports it equally well.
Brands including Midea, Whynter, LG, and DeLonghi all build self-evaporating portable models, so this feature is not tied to venting through a window specifically.
A small amount of condensate can still collect in very humid rooms even on a self-evaporating unit. Check the manual for an overflow drain port in case the internal evaporation cannot quite keep up on the muggiest days.
Energy efficient venting and running cost
An ENERGY STAR rated, energy efficient unit still delivers a lower running cost through a wall vent or sliding-door kit, since the rating reflects the compressor and refrigerant system, not the hose route. Sealing whichever opening you use tightly matters more for the bill than which opening you pick.
Remote control and spot cooling one room
A remote control lets you fine-tune spot cooling for a single windowless room from wherever you are sitting, without walking over to adjust the unit. Pairing that with a well-sealed vent kit is what actually determines how well a room without a nearby window cools down.
Set a timer through the remote control to run spot cooling only while the room is occupied, rather than all day. That single habit change saves more than most hardware upgrades, no matter which vent path the unit uses.