🗓 Updated July 26, 2026 · EcoBack editorial team
Compiled from public tests & customer reviews — not tested by us. Prices vary; check the current price on Amazon. Illustrations, not product photos.
De'Longhi Pinguino PAC EX105
Strong cooling, often in the test-winner line.
Comfee MPPH-09CRN7
Affordable for small bedrooms & offices.
It draws in warm room air, cools it and returns it — the waste heat leaves through the window hose. Real cooling, not just moving air around.
Why venting is non-negotiable
A compressor AC doesn't "make cold" — it moves heat. Everything it pulls out of the room air, plus the electrical waste heat of the compressor itself, leaves through the exhaust hose. Run the unit with the hose lying in the room and you have a very expensive fan heater with extra steps: guides that have measured or documented this consistently conclude an unvented portable AC leaves the room the same temperature or slightly warmer (see for example the venting overview at LearnMetrics).
The 5 real routes, compared
| Route | Renter-safe? | Effort | Catch |
|---|---|---|---|
| Door seal kit (hallway, stairwell or adjoining room) | ✅ Yes | 15–30 min | The adjoining space absorbs the heat — fine for a stairwell, bad for the bedroom next door |
| Balcony / French door, tilted + seal | ✅ Yes | 15–30 min | Same technique as a tilt window; needs a door that opens |
| Through-wall vent (core-drilled, outside grille) | ❌ Permission needed | Trade job | Permanent hole; but the best airflow of all routes |
| Utility room / drop ceiling | ⚠️ Depends | 30–60 min | Heat has to go somewhere — only works if that space is big, unused and ideally ventilated |
| Chimney flue (unused) | ❌ Professional only | Trade job | Must be checked and approved by a chimney sweep first — never improvise this |
Route 1: the door seal kit (start here)
This is the same fabric-and-zip principle as the window kits our tilt-and-turn window guide recommends — just cut for a door frame. You tape or velcro the fabric around the frame, zip the hose through, and the door can still be opened in an emergency.
- Pick the right door. Best: a door to a stairwell, hallway or large unused room. Worst: the door to the room where someone sleeps — you'd be heating it.
- Measure first. Kits are sized for standard door frames (roughly 210 cm height); measure your frame and the hose diameter before ordering.
- Seal honestly. Gaps let the hot air circle straight back — the seal, not the hose, decides how well the room cools.
Fabric kits with zips, sized for door frames — search current offers by name:
Check door seal kits on Amazon →Route 2: a balcony or French door, tilted
If the room has a balcony door but no usable window, treat the door exactly like an oversized tilt window: tilt it, seal the wedge-shaped opening with a fabric kit, and run the hose through the sealed gap. The step-by-step is identical to the tilt-window method — including the mistake of running the unit with the door simply "open a crack", which feeds the exhaust heat straight back inside.
Route 3: the through-wall vent — best airflow, biggest commitment
A core-drilled hole (usually 130–160 mm) with an outside grille and a back-draught flap gives the cleanest, shortest exhaust path and finally frees the window entirely. But it is a permanent alteration: in a rented flat you need written landlord permission, and in an owned flat the exterior wall may count as communal property that requires the owners' association to agree. If you're allowed, it's the one route that turns a portable AC into a semi-fixed installation — and it pairs well with hose insulation, as covered in our hose extension guide.
Routes 4 & 5: utility rooms, ceilings, chimneys — the conditional ones
Utility room / drop ceiling: venting into another indoor space only relocates the heat. That's acceptable if the space is large, unused and ideally has its own ventilation (a storage room with an outside grille, a garage) — and pointless if it's a small closed cupboard, which will heat up until the heat leaks right back.
Chimney flue: an unused flue can technically carry exhaust air, but flues can be shared, blocked, or still serve other flats. In Germany and most of Europe the chimney sweep (Schornsteinfeger) must approve any such use. Never route exhaust into a flue on your own judgement.
The route that usually fails: dryer ducts. Typical portable AC hoses are 125–150 mm across; most dryer wall ducts are narrower. Forcing the exhaust through a smaller duct raises back-pressure, so the unit cools worse, runs longer and can overheat. Only consider it if the duct diameter genuinely matches the hose.
If there is truly no route: stop fighting the physics
A room with no window, no suitable door, no wall you may drill and no approved flue cannot host a compressor AC — and no accessory changes that. The honest alternatives: an evaporative air cooler (no exhaust needed, works best in dry heat, adds humidity), aggressive shading and night-time cross-ventilation, and cooling the person rather than the room. Our German guide to cooling windowless rooms ranks these fallbacks in detail.
Frequently asked questions
Can I run a portable air conditioner without venting it at all?
You can switch it on, but it will not cool the room. A portable AC moves heat from the room air into its exhaust; if that exhaust stays in the room, all the heat — plus the waste heat of the compressor — is released right back, so the room ends up slightly warmer than before.
What is the best venting option in a rented flat with no usable window?
A door seal kit on a door that leads to a hallway, stairwell or another room you don't need cool. It is fabric, attaches with zips or hook-and-loop tape, leaves no damage and needs no landlord permission — the same principle as the window kits, just cut for a door frame.
Can I vent a portable AC into a dryer vent?
Usually not in Europe. Most portable AC exhaust hoses are around 125–150 mm in diameter, while typical dryer wall ducts are narrower, and squeezing the airflow raises back-pressure so the unit cools worse and can overheat. Treat it as a last resort only if the duct diameter genuinely matches.
What if there is truly no venting route at all?
Then a compressor AC is the wrong tool. An evaporative air cooler needs no exhaust hose and helps in dry heat, though it adds humidity and cools far less. Combined with shading and night ventilation it is the honest fallback for a room with no venting route.