Your Home Climate
Running costs

Air conditioning running costs in the UK

What a typical residential air-conditioning split unit actually costs to run during a British summer, broken down by duty cycle, tariff and room type, with the assumptions spelled out.

Editorial confidence
High confidence. Multiple regulator, government or academic sources agree.
Last reviewed
1 June 2026 · next review 1 September 2026

Who this advice is for

Applies to

  • Owner-occupiers of UK homes with a single-room or multi-room split air-conditioning system
  • Households running AC primarily for bedroom comfort during heatwaves and humid nights
  • Households on a standard variable or fixed electricity tariff in 2026

Not intended for

  • Households running portable AC units; the running cost arithmetic is different and considerably worse
  • Commercial cooling loads; the duty cycle and tariff structure do not transfer

You may not need to read the rest of this page

You probably already have enough to act if:

  • You wanted a defensible running-cost range before committing to install
  • You wanted to understand which assumption (duty cycle or tariff) actually drives the bill
Open the AC running cost calculator

This is probably the wrong page for you if:

  • You are weighing a portable AC unit; the arithmetic and the comfort outcome are both considerably worse
  • You need commercial cooling sizing; that is a different scope

Typical bedroom split SEER (cooling efficiency)

6.0 to 8.5

Source: Federation of Environmental Trade Associations · Manufacturer-tested seasonal energy efficiency ratio for current R32 inverter splits in the 2.5-3.5 kW class; a SEER of 8 means 8 kWh of cooling per 1 kWh of electricity over the season.

Ofgem electricity price cap for January 2026, single-rate

≈ 26.9 p/kWh

Source: Office of Gas and Electricity Markets · Headline cap rate used as the reference unit price; actual tariff rates vary and an Economy 7 night rate makes overnight bedroom cooling materially cheaper.

Bedroom split typical electricity draw, hot summer night

0.25 to 0.55 kWh per hour

Source: Federation of Environmental Trade Associations · Indicative inverter-modulated draw for a 2.5-3.5 kW unit holding a bedroom at 22-24 °C overnight; the unit runs at a fraction of its rated input most of the time.

What to do, and why first

01

Set the thermostat to 22-24 °C, not 18 °C

Why this comes first

Every degree below 24 °C roughly doubles the duty cycle of an inverter split during a British heatwave; the unit modulates harder to chase the lower setpoint and the running cost rises faster than the comfort gain. CIBSE summer comfort criteria treat 22-24 °C as the high end of acceptable bedroom comfort; pushing below that is paying for a freezer rather than a bedroom.

Evidence

CIBSE TM59 and FETA guidance both treat 22-24 °C as the upper end of acceptable bedroom comfort; manufacturer duty-cycle curves rise steeply below that setpoint.

CIBSE · CIBSE TM59 · FETA

Confidence

High confidence. Multiple independent sources agree on the direction and the order.

Exceptions
  • Medical conditions where a clinician has recommended a lower setpoint
Next step
Open the AC running cost calculator
02

Match the electricity tariff to when you actually use the cooling

Why this comes first

Households who run AC mostly overnight save more by moving to an Economy 7 or off-peak tariff than they ever save from upgrading to a higher-SEER unit. Households who run AC mostly in the late afternoon during work-from-home heatwaves get the opposite answer; a flat-rate tariff usually wins. The tariff is a one-week decision that outweighs years of efficiency arithmetic.

Evidence

Ofgem-published price-cap rates and Octopus Energy tariff documentation set out the difference between standard, Economy 7 and time-of-use rates that drive overnight AC running cost.

Ofgem · Octopus

Confidence

High confidence.

Exceptions

No common exceptions in UK homes.

Next step
Read the AC bedrooms guide
§01

The two numbers that decide the bill

Two numbers decide the running cost of a residential air-conditioning unit in a British summer: the duty cycle (how many hours the compressor actually runs each summer) and the tariff (what each kilowatt-hour costs at the time it is drawn). Everything else, including the unit's SEER, is a smaller-order correction on top of those two. This piece takes a running-cost view of one product; the broader cooling picture covers whether that product is the right answer in the first place.

A typical 2.5-3.5 kW bedroom inverter split, holding 22-24 °C overnight in a moderately insulated UK bedroom, draws between 0.25 and 0.55 kWh per hour. Multiply by the hours of use and the relevant tariff rate and the picture becomes concrete very quickly.

§02

A worked example for a typical UK bedroom

An eight-hour overnight cycle in a typical 12 m² bedroom during a British heatwave week: roughly 2.5 to 4.4 kWh per night. At the January 2026 Ofgem single-rate cap of 26.9 p/kWh, that is 67p to £1.18 per night, or £8 to £14 across a two-week heatwave. On an Economy 7 overnight rate the same usage often falls below £4 across the same fortnight.

Across a full British cooling season, including the occasional warm afternoon, the realistic annual running cost for a single bedroom split lands between £25 and £85 on a flat tariff, and between £15 and £45 on a sensible off-peak tariff. This is roughly an order of magnitude lower than the running cost of a portable AC unit doing the same job.

§03

Where households spend more than they should

Three patterns account for almost every household who finds the running cost higher than expected. First, the setpoint is below 22 °C, which forces the inverter to modulate harder for diminishing comfort returns. Second, the unit is cooling rooms that nobody is using because the install put one unit per floor instead of one unit per occupied room. Third, the filter has not been cleaned in two summers and the unit is now drawing more electricity to deliver the same effect.

None of these are unit-quality problems. They are commissioning and habit problems, and they are all reversible inside an afternoon.

Evidence behind this page

Every recommendation on this page is traceable to its source. Click a publication to read the original.

  • Government guidance

    Used because it sets the legal minimum standard for new work in the UK and defines the public funding rules homeowners can actually claim.

  • Building standards

    Used because these are the codified design standards UK building services engineers work to; they are written by the profession for the profession.

  • Professional bodies

    Used because these organisations publish independent consumer and technical guidance rather than product marketing.

  • Your Home Climate research

    Used only where no independent published source covers the question, and labelled clearly so readers can weight it accordingly.

    • Your Home Climate editorial

Real homes, public sources

The honesty layer
What we know
  • Manufacturer SEER ranges and inverter duty-cycle behaviour
  • Ofgem unit prices and the tariff structures available in 2026
What varies
  • How many nights per year a specific household actually runs the system
  • How well-insulated the bedroom is and how steady the overnight outside temperature stays
What we don't know
  • The specific tariff terms of your account; the running cost calculator handles that input

The knowledge graph

Technologies
  • Air conditioning
  • External shading
  • Fans & passive cooling
Problems it answers
  • Bedroom overheating in summer
Property types
  • Victorian terrace
  • Loft conversion
  • Modern detached (post-2000)

Sourced from the Your Home Climate knowledge engine; every connection updates centrally.

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