The short answer
A portable air conditioner is a self-contained unit on wheels that cools a room and sends the heat outside through a hose, usually out of a window. It needs no professional installation, but it is noisier and less effective than a fixed split system.
On this page
A portable does the same job as any air conditioner, moving heat from inside your home to outside, but everything is packed into one box in the room with you. That makes it easy to buy and use straight away, and it also explains most of its weaknesses.
How a portable works
Room air passes over a cold coil and comes back out cooler and drier. The heat taken from it goes into a separate stream of air, which the unit pushes outside through a wide, flexible exhaust hose. The compressor, fans and both coils are all inside the cabinet, and most models plug into an ordinary socket.
The moisture removed from the air has to go somewhere. Many models evaporate most of it into the exhaust air, while others collect it in a tank to empty or connect to a drain hose, especially when used as a dehumidifier.
Some portables can also heat. Many use R290 (propane) refrigerant, which has a very low global warming potential but is flammable, so follow the manual's instructions on where the unit can be used and the smallest room it's suitable for.
Single-hose and dual-hose
Single-hose portables use room air to carry heat away from the hot coil, then blow that air outside. Air leaving the room has to be replaced, so warmer air is drawn back in through gaps around doors and windows, working against the cooling.
Dual-hose portables draw outdoor air in through one hose, use it to carry the heat away and send it back out through the other. They pull far less warm air into the room.
| Single-hose | Dual-hose | |
|---|---|---|
| Air that carries the heat out | Room air | Outdoor air |
| Draws warm air into the room | Yes | Much less |
| Choice of models | Wide | Narrower |
Venting the hot air
The exhaust hose usually goes out of a window through a window kit: a panel for a sliding or sash window, or a fabric seal that fits around an opening casement, a type of window common in UK homes. A few things help:
- Seal the gap around the hose as well as you can, or warm air, insects and noise come back in.
- Keep the hose as short and straight as the instructions allow. It gets warm and gives heat back to the room, and a long or kinked hose makes the unit work harder.
- Think about security if a window has to stay partly open, particularly on the ground floor or overnight.
- A permanent vent through a wall is neater, but it's building work, and in a rented home or a flat you'll usually need permission first. See air conditioning in rented homes.
Size ratings
Portables are usually sold by BTU, commonly from around 7,000 to 14,000 BTU (roughly 2 to 4 kW), and kW and BTU explained shows how the two convert. Real-world cooling, especially from a single-hose unit, is usually less than the rating suggests, because of the warm air drawn into the room and the heat given off by the hose. A portable and a split system with the same figure on the label won't cool a room equally.
What a portable does well
- No installation. You set it up yourself, with no engineer, no outdoor unit and no planning permission, because it isn't a fixed installation.
- It moves. It rolls from room to room, although it's heavy on stairs, and it comes with you when you move home.
- It suits renters and homes where a fixed system isn't allowed or practical.
- No refrigerant work. The refrigerant circuit is sealed at the factory.
- Extra modes. Many models can also run as a dehumidifier or a fan.
Where a portable falls short
- Noise. The compressor is in the room with you, so a portable is much louder than the indoor unit of a split system. That matters most in a bedroom at night.
- Less cooling for the electricity. A portable usually uses more electricity for each unit of heat it moves out of the room than a split system does, and it may struggle to keep up in a hot, sunny room.
- The hose and the window. It has to sit near a window or vent, and the opening lets some heat back in.
- Space. It takes up floor space, and the length of the hose limits where it can stand.
- Water. Models with a tank need it emptying, more often in humid weather.
If the hose is the main problem, a through-the-wall unit is fixed in place and needs no outdoor unit, though it's also noisier indoors than a split. Fixed or portable compares the options side by side.
Related guides
- Fixed or portable: which is right for youA fixed split system cools better, runs more quietly and can heat efficiently, but needs professional installation and somewhere for the outdoor unit. A portable suits occasional hot spells, renters and homes where a fixed system isn't possible.
- Evaporative air coolersAn evaporative air cooler blows air through a wet pad so that evaporating water cools it. It uses little electricity and needs no hose or installation, but it isn't air conditioning, adds humidity and does little on humid days.
- Through-the-wall units without an outdoor unitThrough-the-wall air conditioners keep all their parts in one indoor unit that draws and expels outside air through two holes in an outside wall. They need no outdoor unit, but are noisier indoors and usually less efficient than a split system.
- Air conditioning in rented homesTenants usually need the landlord's written permission before fitting fixed air conditioning, and a flat's landlord may need the freeholder's consent too. Portable units usually don't need permission, as long as nothing is drilled or altered.