Bedroom air conditioning if you rent your home

A standard UK assured shorthold tenancy prohibits altering the property without written landlord consent. That covers drilling through an external wall, mounting anything to a masonry facade, running a refrigerant pipe through the fabric, and cutting into brickwork for a bracket. In practice that rules out a conventional fixed split, which needs all four.

It does not cover freestanding appliances, temporary window seals, or anything that leaves no trace when you move out. That is the space tenant-friendly cooling lives in.

A portable monobloc sits on the bedroom floor and vents hot air out of a window through a flexible duct. No drilling, no landlord consent needed, and it moves with you when the tenancy ends. It is the most tenant-friendly option and by far the most compromised: single-hose units are inefficient because they pull cool room air out of the window to cool the hot side of the compressor; twin-hose units are better but still noisier than a fixed split and roughly half as efficient at the same room temperature.

A good 2.5 kW twin-hose portable will hold a 12 to 14 m² bedroom around 22°C on a heatwave night, but at 45 to 55 dB(A) indoor noise; audibly louder than a fixed split and often loud enough to disturb sleep. The noise thresholds piece explains why that number matters.

The classic American window unit is uncommon in the UK because British sash and casement windows do not accept the standard American window-unit frame. A small number of manufacturers now sell UK-format window units designed to sit in the sash gap or a temporary bracket, none of which requires landlord consent if installed without drilling. They are quieter than a portable at the same output because the compressor sits outside the room, and cheaper to run for the same reason.

The catch is aesthetics and security. The unit visibly protrudes from the window and the seal is imperfect; both are acceptable in a summer-only install, both are noticeable in autumn.

The newest category, sometimes called a split-portable or pipe-through-window split, puts the compressor in a small unit that sits outside on a balcony or windowsill, connected to the indoor head by a slim flexible pipe running through a temporary window seal. Performance and noise approach those of a fixed split; the install is landlord-friendly because nothing is drilled, glued or permanently attached.

These are the best tenant option currently on the market for a bedroom that genuinely needs cooling. They cost roughly £900 to £1,500 for a decent 2.5 kW unit, roughly midway between a good portable and a fixed split without the install charge. If you plan to rent for another two summers or more, the maths often works out.

It is worth asking. A polite written request explaining that you will pay for a full installation by an MCS-registered installer, that the unit and pipework will remain on removal as an improvement to the property, and that any wall penetrations will be professionally sealed, is more likely to get consent than most tenants assume. Some landlords will agree in exchange for a small rent increase; others will decline outright. Either answer is useful, and it takes ten minutes to send the email.