For the same level of cooling, a properly sized split air conditioner will usually cost less to run than a portable one. However, a portable air conditioner could cost less overall if you only use it occasionally and want to avoid installation costs.
The right choice also depends on how often you cool the room, whether you own or rent and how well each system suits the space.
Quick running-cost comparison
The examples below use a rounded electricity rate of 26p per kWh. Actual costs will vary by model and room.
| Example | Average electricity use | Cost per hour | Eight hours | Eight hours a day for 30 days |
|---|---|---|---|---|
| Efficient split system | 0.7 kW | 18p | £1.46 | £44 |
| Portable unit working hard | 1.2 kW | 31p | £2.50 | £75 |
In this example, the split system saves about £31 over 30 days. Your savings may vary because electricity use depends on the model, room and weather.
Ofgem’s average capped electricity rate for a standard variable tariff paid by Direct Debit is 26.11p per kWh from July to September 2026 and 26.32p from October to December. These figures cover England, Scotland and Wales. Check the latest Ofgem unit rates or use the rate on your own bill. Northern Ireland has a separate market, with current tariffs listed by the Consumer Council.
Why split systems usually cost less to run
A portable air conditioner has the compressor, fan and other main parts inside the room. It sends hot air outdoors through an exhaust hose, usually fitted into a partly open window.
That arrangement is convenient, but it can reduce efficiency. The hose becomes warm, gaps around the window can let heat back in and a single-hose unit may draw warmer air into the room.
A split system places the compressor outside and connects it to an indoor unit. The windows can remain closed and the heat travels outdoors through refrigerant pipes instead of a large warm hose.
Many modern split systems also use inverter technology. Once the room reaches the selected temperature, the system can reduce its output instead of repeatedly running at full power. This can make it both quieter and cheaper to run.
When a portable air conditioner may cost less overall
Running cost is only one part of the decision. A portable unit needs no permanent outdoor unit or refrigerant pipework. You can buy it, fit the window kit and move it between suitable rooms.
That can make a portable model cheaper if you cool one room for only a few days each year. It may also suit renters or homes where permanent changes are not allowed.
However, moving one unit around does not mean it can cool several closed rooms at once. It still needs a suitable window for the hose each time you use it.
Purchase and installation costs
Portable air conditioners usually cost less to buy. A split system costs more because the price includes outdoor equipment and professional installation. Longer pipe runs, difficult access and extra electrical work can increase the quote.
The higher upfront cost may make sense with regular use. The more hours the system runs, the more opportunity an efficient split unit has to recover part of that difference.
Installation is not a DIY job when work involves F gas. GOV.UK states that people who install, service or maintain this equipment must hold the correct F-gas qualifications.
Our UK installation-cost guide shows what a fitted quote should include.
Noise, windows and everyday use
A portable unit keeps its compressor in the room, so it is usually louder at night. A split system moves the noisiest component outside, although the position of the outdoor unit still needs careful thought.
Portable units also take up floor space and need a hose near a window. Some collect water that must be drained, although many evaporate most of it through the hose. A wall-mounted split unit leaves the floor clear and is ready whenever you need it.
Whichever type you choose, clean the filters as the manufacturer recommends. Keep the outdoor unit of a split system clear of leaves and other debris.
For night-time sound levels, read our bedroom portable-versus-split noise guide.
How to compare models fairly
Start with systems that provide the right cooling capacity for the room. Capacity may appear in kW or BTU/h, but it is not the same as electricity consumption. A 3.5 kW cooling system does not normally draw 3.5 kW of electrical power.
Check the specification or energy label for rated power input, cooling efficiency, sound level and annual energy use. Higher efficiency means more cooling from each unit of electricity.
Be careful when one product shows EER and another shows SEER. EER measures efficiency under set test conditions, while SEER represents performance across a cooling season. You cannot compare the two figures directly. The UK government’s energy label service shows the information used on air-conditioner labels.
Which type is right for your room?
For a bedroom used every summer
A quiet, correctly sized split system will usually be the better long-term choice if installation is possible. Its lower indoor noise and reduced running cost matter when it operates for many nights.
For occasional heatwaves
A portable model may be enough if you only need short-term relief. Fit the window kit as tightly as possible, keep the hose short and close doors to the rest of the home.
For a living room or open-plan area
A split system will generally provide more effective, quieter cooling for a larger space. Whichever type you choose, include connected areas, windows, sunlight and ceiling height when sizing it.
Estimate the cost for your home
Generic examples cannot account for your exact system, room, schedule or electricity rate. CostToCool offers two free ways to get a more useful estimate.
If you already have air conditioning, use Calculate my current setup. Enter the system and how you use it to estimate the cost per week, 30 days and cooling season.
If you have not bought a system yet, choose Plan cooling for my home. It estimates the capacity each area needs and what the recommended setup could cost to run.
Both calculators are free. The result is still an estimate, but it reflects your home and choices instead of relying on one national average.