The Short Answer
If you'll run it a lot, we'd buy a split rather than a portable. A 3.5kW wall-mounted split costs about 19.9p an hour at its rated output, on Daikin's figures for its current Perfera. A 12,000 BTU portable such as Meaco's Cirro costs about 35.5p an hour for similar rated cooling, because it draws 1.8 times the power.
Run either at that output for eight hours a day for a month and that's £48 for the split and £85 for the portable. Real bills should be lower, because once the room is cool the unit slows down or its compressor stops, though on the hottest days an inverter split can boost above its rating and use more.
Work Out Your Running Cost
Air conditioning running cost
What will it cost to run?
From the manufacturers' published figures (for a split, its power worked out from Daikin's EER), at the 1 October to 31 December 2026 price cap rate unless you change it.
An hour at its rated output
19.9p
It draws 0.76kW to give 3.5kW of cooling (worked out from Daikin's EER of 4.63 for its FTXM35A / RXM35A). On the hottest days it can boost to 4.4kW of cooling and draw more.
Your summer at rated output
£48
240 hours at its rated output. An inverter split slows down once the room is cool, so it usually uses less than this; boosting on a very hot day uses more.
The energy label's year
£35
132kWh, Daikin's figure: the label counts 350 hours a year at full output and divides by the seasonal efficiency (SEER 9.25, class A+++). The label uses the same hours in every country, so treat it as a yardstick, not a UK forecast.
Electricity only, at the unit rate; the standing charge is the same whether it runs or not. Bigger rooms, sunny windows and hotter days make it work harder.
Cost per Hour
What an air conditioner costs to run is the electricity it draws times your unit rate. Manufacturers publish the cooling output and the power it takes (or the efficiency, EER: cooling out divided by electricity in), so you can work it out exactly. The split figures below are Daikin's own for its current Perfera wall-mounted range. At 26.32p per kWh, the 1 October to 31 December 2026 price cap rate (the Great Britain average for direct debit; Northern Ireland isn't covered by the cap):
| Unit | Rated cooling | Power at rated output | Per hour | 8 hours a day for 30 days |
|---|---|---|---|---|
| Daikin Perfera FTXM25A / RXM25A | 2.5kW | 481W | 12.7p | £30 |
| Daikin Perfera FTXM35A / RXM35A | 3.5kW | 756W | 19.9p | £48 |
| Daikin Perfera FTXM50A / RXM50A | 5.0kW | 1,359W | 35.8p | £86 |
| Meaco Cirro 12000 BTU | 3.5kW | 1,350W | 35.5p | £85 |
Those are the costs at the rated output the whole time. Real bills should be lower: when we checked in October 2026, the Energy Saving Trust put a typical portable at £4.62 to £5.00 for 24 hours' use in Great Britain, against £8.53 for the Cirro at full power for 24 hours.
An inverter split slows down once the room reaches temperature and speeds up when it's struggling: Daikin's 2.5kW Perfera, for example, runs anywhere from 0.9kW to 3.8kW of cooling, and its 3.5kW goes up to 4.4kW. So on a warm evening it may use a fraction of the figure above, and on the hottest afternoon, in a sunny room, more.
Electricity prices change every quarter, and on a time-of-use tariff your rate depends on when it runs. Put your own rate into the calculator.
Why a Split Costs Less Than a Portable
A portable air conditioner sits entirely in the room and vents its hot air out through a hose. Meaco's Cirro 12,000 BTU portable draws 1,350 watts for 12,000 BTU of cooling. That's about 3.5kW, an EER of about 2.6 on our conversion. Meaco publishes the energy rating (A) but not the kW or EER, and says it's out of stock until March 2027. Daikin's 3.5kW Perfera split, with its outdoor unit outside, has an EER of 4.63. The energy label classes portables and splits differently (on EER for portables, seasonal SEER for splits), so the comparison is approximate.
The energy labels show the gap too. For portables (single duct units), class A starts at an EER of 2.60 and the top class, A+++, at 4.10. Split units are rated on seasonal efficiency instead, and A+++ needs a SEER of 8.50: Daikin's 2.5kW Perfera is 9.47 and its 3.5kW 9.25.
If you only need cooling for a few hot weeks a year, the portable's higher running cost may still work out cheaper than paying for a split system to be fitted. Our installation cost guide has a cost estimator.
Reading the Energy Label
A split unit's energy label shows a yearly cooling figure in kWh. The rules work it out as 350 hours a year at full design output, divided by the unit's SEER, and use the same 350 hours whichever country the unit is sold in. For Daikin's 2.5kW Perfera that's 92kWh (Daikin's figure), or £24 a year at today's rate. Use it to compare units, not as a forecast of your bill.
The 2.5kW and 3.5kW Perfera are A+++ for cooling and the 5kW A++: larger units in the same range are less efficient. So we'd buy the size the room needs, not the biggest: a unit that's too big costs more to buy, and one that's too small works at full output on hot days and still struggles.
How We'd Run It
- Keep the heat out first. Curtains and blinds shut on sunny windows during the day, windows shut while it's hotter outside, and opened once it's cooler. It costs nothing and means the unit has less heat to shift. Our guide to keeping your house cool has the plan.
- Close the door and windows of the room you're cooling, so it isn't cooling the rest of the house too.
- Don't set it as cold as it goes. We'd pick a comfortable temperature, not the coldest, so it gets there and eases off. An inverter split slows right down once the room reaches the temperature you've set (Daikin's 2.5kW runs as low as 0.9kW of cooling).
- If you'll use it a lot, buy a split, not a portable, and an A+++ one: the running cost gap above adds up over a summer.
- Use the timer to cool a bedroom before bed instead of running it all day.
- With a portable, seal the hose. The Energy Saving Trust says gaps where it goes out of the window let warm air back in. It also says to unplug it at the wall when it's off.
If the unit also heats, it's a heat pump. Daikin rates the 2.5kW and 3.5kW Perfera at a heating SCOP of 5.20, meaning about 5.2 units of heat for each unit of electricity over a season, against one for a plug-in electric heater. See our air-to-air heat pump guide.
Get air conditioning quotes
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