The honest case for portable units; and the honest case against.

A single-hose portable expels hot air through one hose. The replacement air comes from… inside your house. Which means it sucks warm outside air back in through every crack to balance the pressure. You're effectively cooling outdoor air. Single-hose units typically deliver 40–50% of their rated capacity in practice.

A dual-hose portable draws outside air through one hose, uses it to cool the condenser, and expels it through the other. The room stays sealed. Same compressor, same refrigerant, same shell; but 2x more effective at cooling the room. Always specify dual-hose.

The reason single-hose units still dominate the shelves is price: a dual-hose unit is typically £100–£200 more. It's the cheapest £150 you'll spend on summer comfort.

Most portable ACs ship with a flimsy plastic window panel that fits sash windows badly and casement windows worse. Every gap around it leaks warm air straight back into the room. We've measured rooms where sealing the kit properly dropped temperatures by 3–4°C with no change to the unit itself.

If you're committing to a portable for the summer, spend an afternoon and £30 on proper foam sealing, weatherstripping around the panel, and a cover for the sash gap above. It's the difference between a unit that works and a unit you'll resent.

A premium portable AC at maximum speed sits at 52–58 dB(A); roughly the volume of a normal conversation, measured at the unit. Half a metre away from your bed at 3am, that is loud. The compressor is in the room with you.

A wall-mounted split puts the noisy compressor outside. The indoor unit runs at 19–25 dB(A) on sleep mode; quieter than a fridge. For bedroom use, this is the entire reason splits exist.

If you must use a portable in a bedroom: cycle the unit (cool the room hard before bed, switch off to sleep), or fit a long enough hose that you can put the unit in a hallway and pipe cool air in.

Portable wins when: you rent, your problem is one room for a few weeks a year, you have nowhere to fit a split's outdoor unit, or you're testing whether you'd benefit from AC before committing to install. £400–£700 for a decent dual-hose unit, set up in an afternoon, sold on eBay in October.

Portable loses when: you own the house, you're spending £500+, the same room needs cooling every summer for the next decade, or you care about sleep quality. The lifetime running and electricity cost of a portable in heavy use exceeds a split's full install cost within 3–4 summers.