How much does a portable air conditioner cost to run?

A 1,000 W portable AC costs about 26p an hour at the Ofgem cap; Which?’s tested units average 22p an hour. Work out your cost per hour, night and summer.

By the Wisiko editorial team · Published 14 October 2026 · 4 min read

Enter your unit’s input power — or the figure on its energy label, or its BTU rating and class — and how long you run it. The calculator shows the cost per hour, per day and per season at the UK price cap, the US average or your own unit rate.

BTU, cooling kW and watts: what actually costs money

A portable air conditioner’s spec sheet lists two different powers:

• Cooling capacity (BTU/h or kW): how much heat it removes from the room.
• Input power (W): how much electricity it draws. This is what you pay for.

The ratio between them is the EER (energy efficiency ratio). For single-duct portable units, the energy label used in the EU and Great Britain sets the classes by EER: A from 2.60, A+ from 3.10, A++ from 3.60 and A+++ from 4.10 (Regulation 626/2011). With 1 kW = 3,412 BTU/h:

These are label test conditions; real efficiency changes with the outdoor temperature. Which?, which buys and tests the portable units sold in the UK, found some models using up to 16% more energy than their label suggested. Trusted Reviews gives two real examples: one 2.5 kW unit drawing 700 W (EER 3.57) and a 9,000 BTU unit drawing 1 kW (EER 2.6).

On the label itself, hourly consumption is shown in kWh/60 min, rounded up to a whole number — a 0.8 kWh/h unit shows “1”. The product fiche gives the exact value.

Cost per hour, per night and per summer

Which? reports that the portable air conditioners it tested cost 22p an hour on average on their highest setting, from 17p to 31p, at the 26.32p/kWh cap — about 0.65 to 1.2 kWh per hour.

A unit doesn’t run flat out all the time, though. Once the room reaches the set temperature, the compressor switches off and back on, or slows down on inverter models. In Trusted Reviews’ testing it took about two hours to cool a bedroom in the evening, after which the compressor needed to run 25–50% of the time. For an 8-hour night with a 1 kW unit, that is 3.5–5 kWh: roughly 92p to £1.32 at the price cap, or 64¢ to 92¢ at the US average. Use the “time at full power” field to model this.

What real homes use

ADEME, France’s energy agency, metered appliances in 100 homes for a year (July 2023 – July 2024). Its 11 portable air conditioners used a median of 31 kWh a year (mean 70 kWh; the top quarter above 130 kWh) — mostly occasional use during heatwaves. At the other end, ADEME quotes an EDF R&D survey figure of about 710 kWh a year for a portable unit, which is what daily summer use looks like. The 15 electric fans in the same panel used 7 kWh a year (median).

Five ways to cut the cost

1. Keep heat out first: close curtains and blinds in the day and windows when it is hotter outside, as Which? recommends.
2. Don’t set the minimum temperature: Trusted Reviews suggests about 21–24 °C as the lowest sensible target; below that the unit never reaches it and runs non-stop.
3. Seal the window gap around the hose with a window kit if your window type allows — warm air coming back in through the opening is a key weakness of single-duct units (ADEME and Which? both flag it).
4. Pre-cool, then switch to a fan for the night.
5. Size it and rate it right: an undersized unit runs constantly, and at the same capacity an EER of 3.1 (A+) or 3.6 (A++) draws about 16% or 28% less than 2.6 (A).

Many portable units can also run as a dehumidifier — see our dehumidifier running cost guide. For any other appliance, use the appliance running cost calculator, and if you only know amps or watts, the watts vs kilowatt-hours explainer helps.