Cool a garage conversion as the living space it now is, after you know the insulation and the damp. The decision is whether this room, used as a sitting room, bedroom or study, can hold a setpoint in a shell that used to be a garage. Survey the walls, the slab and the new glazing. Do not copy a commercial gym design, and do not hang a unit where the old door opening is still a weak wall. An F-gas certified company installs the pair once the fabric and the outdoor spot are real.
A sofa where the car used to stand
If the conversion is finished, it should have insulation, a damp strategy and a proper floor. Cooling then follows the room you furnished: a bedroom wants the air off the bed, a sitting room wants it off the sofa. Say the garage is now living space, whether it is insulated, what the room is for, and whether the old door opening is now glass. Photos of the side walls, the outside flank, any damp staining and the consumer unit show the shell. Door shut to the house means this is its own zone. This is a furnished living space. Size the sofa, the bed or the desk, not a workout load.
Insulation before a bigger kilowatt
If the walls are still single-skin brick and the roof is the old felt, fix that conversation first. A split will take the edge off a hot afternoon and will not turn a cold garage into a dry living room by itself. Yes, insulate before you buy the unit if the walls and roof are still bare garage fabric. Cooling helps a hot day either way, and it will not correct a cold, damp shell through the winter on its own. Say if insulation is still missing, so nobody prices a finished-room duty for a bare shell.
The pier where the up-and-over door was
The old up-and-over opening is often a new window wall with little solid pier. The indoor unit needs a side wall that is actually masonry or a lined stud with a fixing.
- Confirm insulation before chasing a bigger kilowatt.
- Place the unit for the sofa or the bed, not the old car bay.
- Avoid the thin pier where the garage door was.
- Give it its own circuit from the house board.
Condensate on a slab that never had a gully
Cooling a damp, poorly detailed conversion will mark cold corners. The split's own condensate must go to a drain or a pump, not onto the floor you walk on. A garage slab that never had a gully needs a route designed, not a hole in the mortar. The outdoor unit can stand on a pad beside the conversion if the flank wall is too weak or too close to the boundary. On a proper pad beside the conversion, yes, if airflow, drainage and Planning Portal conditions work. Not on the new window wall, and not in the only path to the garden. In England, Planning Portal conditions apply, and the neighbour who used to ignore a garage may notice a condenser. Keep airflow off their path.
A small board and a picture window
Garage consumer units are often a small enclosure fed from the house. A dedicated 230 V circuit for the split has to be confirmed by someone competent. Do not share a socket with a tumble dryer that stayed behind. Size the furnished room and its glass, not the old parking area. A single-skin south wall with a new picture window is a larger duty than a lined box. As a 2026 illustration, a converted garage with a proper wall and a short pipe is often in the low thousands including VAT. Damp repairs, a new circuit from the house and a pump are the items that sit outside that illustration. Ask for one single split with model codes, a note on whether the wall can take the bracket, and the condensate route.
When the shell is still a garage, or the load was a gym
Do not copy a commercial gym design onto a sitting room, bedroom or study. If the walls and roof are still the old garage fabric, the split is not the first job. A unit hung on the thin pier where the garage door was, or priced as a finished room while insulation is missing, is the wrong approach for this shell.
Core buying guides
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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.