A portable air conditioner is a cooling unit on wheels that plugs into a socket and vents its heat out of a window through a hose. It needs no installer or outdoor unit, so it suits renters, short-term needs and rooms where a fixed system is not possible. A 3.5 kW (12,000 BTU) unit suits a typical bedroom or living room, though a split system is quieter and cheaper to run.
Here is how to choose one in the UK: what size you need, single or dual duct, why almost every portable now uses propane, what they cost to run, and how to get the most out of one.
Portable air conditioners at a glance
| Question | Short answer |
|---|---|
| What size do I need? | About 3.5 kW (12,000 BTU) for a typical bedroom or living room. Larger, sunnier or busier rooms need more |
| Single or dual duct? | Single duct is simpler and most common. Dual duct cools more effectively because it does not pull warm air back into the room |
| Which refrigerant? | Usually R290 (propane), because HFCs with a GWP of 150 or more have been banned in new movable air conditioners since 2020 |
| Running cost? | Roughly 26p to 35p an hour at full output at the current price cap, depending on size and efficiency |
| Installation? | None. Plug it in and fit the hose to a window kit |
| Planning permission? | Not needed |
Sizing: kW and BTU
Portable units are sold by cooling output, in kilowatts or British thermal units per hour. One kilowatt is about 3,412 BTU per hour, so a 3.5 kW unit is roughly 12,000 BTU. The output on the box is the cooling it delivers, not the electricity it draws.
As a guide, the 3.5 kW portables we sell are rated to cool up to about 30 to 35 square metres, depending on the model, the insulation, the number of people in the room and how much sun it gets. A loft room with roof windows, a south-facing room with large glazing or a home office full of computers needs more cooling than its floor area suggests. For large or open-plan spaces, a portable will struggle, and a fixed system is the better answer.
Single duct or dual duct
A single-duct portable draws air from the room, uses it to carry heat away from the compressor, and blows it out of the window. Because room air is being pushed out, warm air is drawn back in through gaps around doors and windows, and some of the unit's effort goes on cooling that.
A dual-duct portable takes outside air in through one hose and sends it back out through the other, so it does not depressurise the room. It cools more effectively for the same output, but it is bulkier and needs a window kit that takes two hoses.
The energy label reflects how these units work. Under the UK labelling rules, single and double duct units are rated on EER, their efficiency at full output, and a single-duct unit shows its consumption per hour rather than per year. A single-duct unit needs an EER of 3.10 or more to reach A+.
Why portables use propane
The retained F gas regulation bans movable room air conditioners, defined as hermetically sealed equipment the user can move between rooms, from containing HFCs with a GWP of 150 or more, from 1 January 2020. That rules out the HFCs used in fixed systems, so portables now use R290, propane, a natural refrigerant with a very low GWP.
Propane is flammable, which is why portable units hold small sealed charges and come with clear instructions. Keep the unit upright, follow the manufacturer's guidance on room size and ventilation, and never try to open or regas the sealed system.
Running costs
Portables are less efficient than split systems, mainly because the compressor and its heat are in the room. At the Ofgem price cap rate of 26.32p per kWh for 1 October to 31 December 2026:
| Unit | Electricity drawn at full output | Per hour | Per 8-hour day |
|---|---|---|---|
| 2.6 kW single duct, EER 2.6 | 1.00 kW | 26.3p | £2.11 |
| 3.5 kW single duct, EER 2.6 | 1.35 kW | 35.4p | £2.83 |
| For comparison: 3.5 kW split, SEER 7.0 | 0.50 kW | 13.2p | £1.05 |
Check the EER on the label of the model you are considering and use your own unit rate. Our guide to air conditioning running costs explains the sums in more detail.
Noise
Because the compressor is in the room, a portable is always louder than the indoor unit of a split system. The units we sell are rated at around 51 to 55 dB at full power, and like most portables they have a sleep mode that turns the noise down at night. If the room is a bedroom and you are a light sleeper, that is worth weighing before you buy.
Getting the most out of a portable
- Seal the window properly. Use the window kit and close any gaps around it, or warm air pours back in around the hose.
- Keep the hose short and straight. A long or kinked hose makes the unit work harder and can overheat it.
- Close the door. Cool the room you are in, not the landing.
- Draw the blinds. Sun through glass is often the biggest load in a UK room in summer.
- Clean the filters. Every couple of weeks in heavy use, following the manual.
- Deal with condensate. Some units evaporate most of it, others need emptying or a drain hose, especially in humid weather.
Portable or split system
A portable is the right answer when you rent, need cooling for a few weeks a year, or cannot fit an outdoor unit. A wall-mounted split is better for a room you want cool every summer: it is quieter, cheaper to run, cools more evenly and can heat efficiently in spring and autumn. Our comparison of split and portable air conditioning goes through the trade-offs in detail, and a split needs to meet the planning rules for air conditioning where a portable does not.
Questions people ask about portable air conditioners
What size portable air conditioner do I need?
For a typical bedroom or living room, about 3.5 kW, or 12,000 BTU. The 3.5 kW units we sell are rated for up to about 30 to 35 square metres. Sunny, poorly insulated or busy rooms need more cooling, and large open-plan spaces are better served by a fixed system.
Do portable air conditioners work?
Yes, for single rooms of a sensible size, as long as the window kit is sealed and the door is closed. They are less efficient and noisier than split systems, and a single-duct unit pulls some warm air back into the room, so set expectations accordingly in a heatwave.
How much does it cost to run a portable air conditioner?
At the October to December 2026 price cap of 26.32p per kWh, a 2.6 kW unit with an EER of 2.6 costs about 26p an hour at full output, and a 3.5 kW unit with the same EER about 35p. Check the label of the exact model.
Do portable air conditioners need to be vented?
Yes. Every portable air conditioner has to send the heat it removes outside, usually through a hose to a window kit. A unit without a hose to the outside is an evaporative cooler or a fan, not an air conditioner.
Can a portable air conditioner heat a room?
Some can. Models with a heat pump mode heat as well as cool, which makes them useful in spring and autumn, but they are less efficient at heating than a reversible split system.
Do I need planning permission for a portable air conditioner?
No. A portable that vents through a window kit is an appliance, not a change to the building, so planning permission does not apply.
Choosing your unit
If a portable is the right answer for your room, you can see the 3.5 kW cooling-only and heating-and-cooling units we sell here. If you would rather have a quiet, fixed system for a room you use every summer, see our home air conditioning installation service.
Last updated: 4 November 2026
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.