Is a window air conditioner cheaper to run than a portable?

Yes. A window unit exhausts heat straight outside and doesn't lose conditioned air the way a single-hose portable does, so it draws roughly 15–25% less power for the same BTU. On a 12,000 BTU unit that's about £0.28/hr for a window vs £0.35/hr for a portable in the UK.

Should I buy a portable or window air conditioner?

Choose a window unit if you have a suitable sash window or wall opening and want lower running cost and noise for one room. Choose a portable if you can't fit a window unit, have tilt/turn or casement windows, rent, or need to move cooling between rooms.

Why are portable air conditioners less efficient than window units?

A single-hose portable pushes warm air out of a hose, creating negative pressure that pulls hot outdoor air back into the room through gaps. A window unit sits in the opening and rejects all its heat directly outside, so none of the cooled air is wasted.

Portable vs Window Air Conditioner: Which Is Cheaper to Run?

Published: May 25, 2026

Portable and window air conditioners are the two no-installer options — neither needs a refrigerant engineer. The split between them comes down to your windows: if you have an opening a window unit can sit in, it’s cheaper to run and quieter; if you don’t, a portable is your route to cooling.

Side by side (12,000 BTU)

	Portable	Window
Typical efficiency (EER/CEER)	~8.5	~10.5
Power draw	~1,400 W	~1,140 W
Cost/hr — UK @ £0.245	£0.35	£0.28
Cost/hr — US @ $0.16	$0.23	$0.18
Install	Vent hose, plug in	Mount in window/wall opening
Noise	50–65 dB (in-room)	50–60 dB (split across the window)
Blocks the window?	Hose only	Yes, fully
Moves between rooms	Easily	No (semi-permanent)

Why the window unit runs cheaper

A window unit sits half in, half out of the opening and dumps all its waste heat straight outside. A single-hose portable, by contrast, blows room air out through the hose — and that air gets replaced by warm, unconditioned air drawn in through every gap in the room. The portable is partly fighting itself, which is why it needs more watts for the same cooling and costs more per hour.

The window unit is also better placed acoustically: the compressor half hangs outside, so less of the noise reaches you than from a portable sitting in the middle of the floor.

Where the portable wins

Your windows won’t take a unit — tilt-and-turn, casement, or no sill (common outside North America). This is the single biggest reason portables dominate the UK/EU market.
You rent and can’t fit anything semi-permanent.
You want to move it between rooms or store it off-season.

The verdict

If you have a US-style sash window (or a wall opening) and you’re cooling one room, a window unit is the better buy — lower running cost, often cheaper to purchase, and it frees up your floor. If your windows can’t take one, or you need flexibility, a portable is the practical choice and pays for that convenience with a higher hourly cost.

Either way, pick a dual-hose model over single-hose if you can — it closes much of the efficiency gap.

Next: single-hose vs dual-hose portables · portable vs window vs split · what size AC do I need?