What is a good cost per hour to run an air conditioner?

It depends on cooling capacity, but as a rough UK guide (24.5p/kWh): a 9,000–12,000 BTU mini-split around 10–18p/hr is good, a window unit 15–25p/hr is fair, and a portable above ~30p/hr is on the expensive side. Compare like-for-like BTU — a bigger unit costs more per hour but may cool faster.

What is a good EER or SEER rating?

For a mini-split, SEER 18+ is good and 20+ excellent; window units are best judged on CEER ~11–12; portables typically sit at EER 8–10, so anything above ~10 is good for that type. Higher is always cheaper to run for the same BTU.

Why do portables cost more per hour than mini-splits?

Portables are the least efficient type (EER ~8–10) because single-hose designs pull conditioned air out of the room, so they draw more watts for the same cooling. Mini-splits (EER/SEER 12–20+) deliver far more cooling per watt, hence a much lower cost per hour.

How do I use these benchmarks with the comparison?

Filter the comparison to your AC type and BTU bracket, then check the cost-per-hour and power columns against the ranges below. A unit at or below the 'good' figure for its type is efficient; well above the 'fair' figure is a money pit over a season.

What's a Good Cost Per Hour for an Air Conditioner? Benchmarks by Type

Published: May 24, 2026

The comparison ranks every unit by cost per hour to run, but a number only means something with a benchmark. Use these typical ranges to judge whether a unit is efficient, average, or a money pit for its type. (Cost figures use the UK average of 24.5p/kWh; scale by your own rate with the running-cost calculator.)

Cost per hour by type (≈9,000–12,000 BTU)

AC type	Typical power	Good (cheap to run)	Fair	Money pit
Mini-split (ductless)	500–1,100 W	≤ £0.15/hr	£0.15–0.25	> £0.28
Window	700–1,100 W	≤ £0.18/hr	£0.18–0.27	> £0.30
Split (fitted)	600–1,100 W	≤ £0.18/hr	£0.18–0.27	> £0.30
Portable	1,000–1,500 W	≤ £0.26/hr	£0.26–0.37	> £0.40

Bigger units (18,000 BTU+) cost more per hour in absolute terms but can be more efficient per BTU — so always compare within a BTU bracket, which the comparison’s BTU filter makes easy.

Efficiency (EER / SEER) by type

Efficiency is what drives the cost above — EER/SEER explained:

AC type	Poor	Good	Excellent
Mini-split (SEER)	< 16	18–20	22+
Window (CEER)	< 10	11–12	13+
Portable (EER)	< 8	9–10	11+

A stated EER/SEER above the “good” column for its type means a unit will run cheaply; below “poor” it’s an energy hog. When a listing doesn’t state efficiency, the comparison estimates the power draw and flags it est. (how we calculate).

Quick rules of thumb

Mini-splits win on running cost — if a fixed install is an option, they’re almost always the cheapest per BTU.
Portables are the most expensive to run — judge them against the portable column, not against mini-splits.
Watch the watts. For the same BTU, fewer watts = lower cost, every hour it runs. The comparison’s Power column is sortable for exactly this.
A small efficiency gap compounds. EER 8 vs 12 on a 12,000 BTU unit is roughly £30+/month different at 8h/day.

The bottom line

Don’t judge an air conditioner by sticker price or BTU alone — check its cost per hour against the “good” figure for its type. Anything at or below it is efficient; well above the “fair” range will cost you all season.

Next: air conditioners ranked by cost to run · SEER vs EER explained · running-cost calculator.