A portable air conditioner exhaust hose carries the hot air your unit pulls out of the room and pushes it outside. Without it vented properly, a portable unit simply moves heat around the same room, so the hose is the single biggest factor in how well it cools.
This guide explains hose diameters and lengths on typical UK portable units, whether you can extend an air con exhaust hose, single-hose versus dual-hose designs, window venting kits, how to fix leaks and kinks, and when a fixed split system removes the hose problem altogether.
- The exhaust hose removes the room's heat — poor venting is the main reason portable units under-perform.
- Typical UK portable hoses are around 13–15cm in diameter and up to about 2m extended.
- Extending the hose beyond the manufacturer's limit cuts cooling and can cause overheating.
- Dual-hose units are more efficient than single-hose designs; both need well-sealed venting.
- A fixed split system has no exhaust hose at all and is the permanent fix for regular cooling.
What the exhaust hose does and why venting matters
Every air conditioner works by moving heat. Inside a portable unit, a refrigerant circuit absorbs heat from the room air at the evaporator and releases it at the condenser. That condenser heat has to go somewhere, and on a portable air conditioner it leaves through the exhaust hose. The air coming out of the hose is often 20°C or more warmer than the room.
If the air conditioner exhaust is left inside the room, or vented into a closed hallway, the unit fights itself: it cools the air at the front and dumps the same heat back out of the back. Poor venting is the most common reason people say their portable air con "doesn't work". A properly sealed hose route to the outside is what turns a portable unit from a noisy fan into genuine cooling.
Because the unit pushes air out of the room, it also creates slight negative pressure, which draws warm replacement air in through gaps around doors and windows. That is why sealing around the hose outlet matters as much as the hose itself.
Hose diameters and lengths on typical UK portable units
Most portable air conditioners sold in the UK use an exhaust hose with an internal diameter of roughly 13cm to 15cm (around 5 to 6 inches). Smaller budget units sometimes use a slightly narrower hose. The hose is usually a flexible, concertina-style PVC or plastic duct supplied at about 1.2m to 1.5m when relaxed, stretching to around 2m.
The ends matter as much as the diameter. Manufacturers fit their own connectors — a twist-lock or clip collar at the unit end and a flat nozzle or round outlet at the window end. These are not standardised between brands, so when buying a replacement air conditioning unit hose, match the diameter and the connector type to your model, ideally using the manufacturer's part.
A short, straight hose always performs best. Every bend, sag and extra metre adds resistance, reduces airflow and lets heat radiate back into the room through the hose wall.
Can you extend a portable air conditioner exhaust hose?
You can fit a longer air conditioning hose, but it comes with a cost. Most manufacturers recommend keeping to the supplied length, and many state a maximum of around 2m to 3m. Beyond that, the fan has to push hot air further, airflow drops, and the hose itself gets hot and leaks heat back into the room.
In practice, a long air conditioning hose leads to lower cooling output, more running time and higher electricity use, plus a greater risk of the unit overheating and cutting out on a thermal safety switch. Some units also begin to show error codes when exhaust airflow is restricted.
If you must extend, use the same diameter, keep joints sealed with a proper coupler rather than tape alone, keep the run as straight and level as possible and insulate the hose where it passes through warm spaces. If you find you need a hose of several metres to reach a window, the room is usually better suited to a fixed system.
Single-hose vs dual-hose portable air conditioners
A single-hose unit takes air from the room to cool its condenser and blows it out through one exhaust hose. It is simpler and cheaper, but because it expels room air it pulls warm outside air in through gaps, which reduces real-world efficiency.
A dual-hose unit uses one hose to draw outside air in to cool the condenser and a second hose to send it back out. The room air is not used for condenser cooling, so there is less negative pressure and less warm infiltration. Dual-hose units generally cool a room faster and more evenly, though they are bulkier and need a larger window opening for two hoses.
Whichever type you have, both depend on short, well-sealed hose runs. Neither design removes the noise of the compressor sitting inside the room.
Window venting kits and tidy venting options
Most units come with an adjustable window slider panel: a plastic strip that fills the gap in a sash or sliding window, with a hole for the hose nozzle. These work well on sash and sliding windows but leave gaps on casement and tilt-and-turn windows common in UK homes.
For hinged windows, a fabric window seal kit — a zipped or hook-and-loop sheet that fixes around the frame — gives a much better seal and lets you close the window onto the hose. Other tidy options include a permanent wall outlet fitted through an external wall with a flap that closes when not in use, or a glazed panel insert with a fixed outlet, both of which give a neater finish for regular summer use.
Avoid simply hanging the hose out of a half-open window; the gap lets heat, insects and rain straight back in and undoes much of the cooling.
Fixing leaks, kinks and damaged hoses
Check the hose whenever cooling drops off. Kinks and tight bends restrict airflow, so straighten the route and keep the hose as short as it will reasonably go. Sags allow condensation to collect; support the hose so it falls gently towards the outlet.
Splits and tears in the concertina wall leak hot air back into the room. A small split can be temporarily sealed with aluminium foil tape, but a replacement hose of the correct diameter and connector is the proper fix. Cracked end collars should be replaced rather than glued, because a poor seal at the unit end blows hot air straight back out.
If water drips from the hose or unit, that is usually condensate rather than a hose fault: empty the internal tank, check the drain plug, and make sure the unit is level. Persistent leaks, overheating or the unit tripping out after a hose has been sorted point to an internal fault worth having checked.
When to call an engineer
The hose is something you can manage yourself, but some issues need specialist advice. If a portable unit runs but no longer blows cold after you have checked venting and filters, if it repeatedly cuts out, or if you see oil marks or ice on internal parts, an engineer can diagnose the fault and advise whether repair is worthwhile.
An engineer can also advise on supply and fitting for both portable and fixed air conditioning — sizing the cooling output for the room, recommending a suitable unit, and explaining running costs. For faults on existing units, see our air conditioning repair service; for routine care, our air con servicing page explains what a service includes.
How a fixed split installation removes the hose problem
A fixed split air conditioning system separates the hot and cold sides completely. The indoor unit sits on the wall and the compressor and condenser sit outside, connected by insulated refrigerant pipework through a small core hole in the wall. There is no exhaust hose, no window kit and no hot air leaking back into the room.
The result is quieter, more efficient cooling, and most modern split systems also heat efficiently in winter as an air-to-air heat pump. Installation must be carried out by an F-Gas certified engineer, and the system takes up no floor space.
If you are relying on a portable unit every summer, stretching a long hose to a window or fighting heat leaks, a fixed system is the permanent fix. See home air conditioning installation for houses and flats, or commercial air conditioning installation for offices and shops, and compare our fixed installation prices.
Frequently asked questions
What size is a portable air conditioner exhaust hose?＋
Most UK portable air conditioners use an exhaust hose with an internal diameter of around 13cm to 15cm, about 1.2m to 1.5m long relaxed and extending to roughly 2m. Connectors vary by brand, so match the diameter and fittings to your model.
Can I make my portable air con hose longer?＋
You can, but cooling falls as the hose gets longer. Many manufacturers advise a maximum of around 2m to 3m. Longer runs reduce airflow, leak heat back into the room and can cause overheating cut-outs.
Does a portable air conditioner have to be vented outside?＋
Yes. The exhaust hose carries the heat removed from the room. If it is not vented outside, that heat is released back indoors and the unit cannot cool the room effectively.
Are dual-hose portable air conditioners better than single-hose?＋
Dual-hose units usually cool faster and more efficiently because they use outside air to cool the condenser, reducing warm air being drawn in through gaps. They are bulkier and need space for two hoses.
How do I vent a portable air conditioner through a casement window?＋
Use a fabric window seal kit that fixes around the frame and lets you close the window onto the hose. Standard slider panels are designed for sash and sliding windows and leave large gaps on casements.
How do I fix a split or kinked air con exhaust hose?＋
Straighten kinks and shorten the route where possible. Small splits can be sealed temporarily with aluminium foil tape, but the proper fix is a replacement hose with the correct diameter and connector for your unit.
Is a fixed split system better than a portable air conditioner?＋
For regular use, yes. A fixed split system puts the hot side outdoors, so there is no exhaust hose or window kit. It is quieter, more efficient and can also heat in winter. It must be installed by an F-Gas certified engineer.
