Do not buy a landing unit as the only cooling for the bedrooms. Closed doors keep the cool air on the stair. Open doors, and the stair drops that air downstairs. Either way the landing leaks the air you wanted in the rooms. Put indoor units in the rooms you shut at night. A landing head can take the edge off the stair itself if that is truly the goal, and it must not rely on propping fire doors. F-gas rules apply. In England, the outdoor unit is a Planning Portal decision.
Cool air falling down the stair
A landing is a corridor with a hole down the middle. Cool air from a high wall unit falls and runs away: under bedroom doors if they are shut, and down the stair if they are open. The sensor on the landing sees a cool hall and stops. The pillows stay warm. That is why a landing is a bad primary cool. One landing unit will not cool all the bedrooms. Closed doors keep the cool air out. Open doors send it down the stair. Put a unit in each room you need cool with the door shut.
Warm air rises, so in heating mode a landing unit can leave you with a hot ceiling and bedrooms that only benefit when doors are left open. Open doors then undo the reason the bedrooms were separate rooms. Do not size one landing unit as if it were three rooms. Cool the bedrooms with units in the bedrooms. Treat a landing unit as stair-only, if you fit one at all.
Fire doors, treads and a stair-only extra
Landings often have fire doors, especially in loft conversions and flats. Those doors are part of the escape. Wedging them open so a hallway unit can cool a bedroom defeats that. If the only way the scheme works is a wedge, the scheme is the wrong scheme. Do not prop fire doors to pass the air. You can choose to leave ordinary bedroom doors open at night, and the stair will still lose air downwards. If the doors are fire doors, do not wedge them. The landing remains a weak primary source. The stair will also steal air in a house with no fire doors at all. Physics does not wait for a closer. Price the bedrooms.
Some households want the stair less stifling on the way to bed, with bedrooms already equipped. A small unit, thrown along the landing and not down the stairwell, can do that limited job. It still will not hold a shut bedroom. A landing unit is worth fitting as a small extra for the stair, once the bedrooms have their own units. Not as the only cooling for the floor. Pipework in a stair needs lids that come off, and a condensate route that does not weep on the treads. The outdoor unit still needs a lawful, quiet spot. Use an F-gas certified company. Read the Planning Portal conditions in England before you add that condenser.
Frequently asked questions
Will one landing unit cool all the bedrooms?
No. Closed doors keep the cool air out. Open doors send it down the stair. Put a unit in each room you need cool with the door shut.
Can I leave the bedroom doors open at night?
You can choose to, and the stair will still lose air downwards. If the doors are fire doors, do not wedge them. The landing remains a weak primary source.
Is a landing unit ever worth fitting?
As a small extra for the stair, once the bedrooms have their own units. Not as the only cooling for the floor.
Core buying guides
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Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.