Air conditioning for loft conversions
A loft conversion is often the hottest room in the house by July. We cool it properly: a unit that suits your roof shape, a pipe route you won't notice and a sensible place for the outdoor unit. If your loft is still being built, we can fit the pipework while the walls are open.
- 5 kW wall unit, inc. VAT
- From £2,450
- pipes in before the plasterboard
- First fix
- for cold winter mornings
- Heats too
- workmanship guarantee
- 2 years
Why lofts overheat
A loft sits right under the roof, which takes the full sun all day. Tiles and slates heat up and pass that heat into the room below. Roof windows let sunshine straight in, often with little shade. And warm air from the rest of the house rises to the top floor.
Good insulation, which building control rightly asks for, slows the heat getting in but also slows it getting out. So a loft that has warmed up during the day often stays warm well into the night. A fan just moves the warm air around. Air conditioning takes the heat out of the room.
Which unit suits your roof shape
Sloped ceilings decide where an indoor unit can go. These are the usual options.
| Loft type | Indoor unit | Outdoor unit |
|---|---|---|
| Roof-light (sloped ceilings, roof windows) | High on the gable or party wall if there's the height. Otherwise a floor console on a low wall | Bracket on the rear or side wall, with pipes down in trunking |
| Rear dormer | High on the dormer's back wall or the party wall, throwing air along the room | On the dormer's flat roof, or a wall bracket |
| Mansard | Near-vertical walls give plenty of space for a high wall unit | On the flat top of the mansard, or the rear wall |
| Hip-to-gable | High on the full-height gable wall, usually the easiest loft of all | Bracket on the gable wall |
| Any loft with a deep eaves or ceiling void | A ducted unit hidden in the void, with only grilles showing. Needs about 300–400 mm of space and service access | Wall bracket or flat roof, decided at survey |
Wall units need clear space above and around them for air to flow. We check the exact clearance for your model at the survey.
Sizing a loft
Lofts need more cooling per square metre than rooms downstairs, because of the roof and the glass. These are starting points, not a substitute for the survey.
| Your loft | Typical floor area | Starting point |
|---|---|---|
| A small room with one or two roof windows | Up to about 15 m² | 2.5 kW |
| A bedroom with an en suite, or a rear dormer | About 15–25 m² | 3.5 kW |
| A large suite or open space with lots of glazing, facing south or west | About 25–40 m² | 5 kW |
| Two separate rooms, such as a bedroom and a study | Any | A multi-split, one indoor unit per room |
A bigger unit isn't better. An oversized unit switches on and off more, is louder and costs more to run. We size each room from its area, glazing and orientation.
Pipe routes and condensate pumps
Each indoor unit connects to the outdoor unit with two copper refrigerant pipes, a cable and a drain pipe, all running together. In a loft the shortest route is usually straight through the wall behind the unit to an outdoor unit on a bracket or the dormer roof.
If the outdoor unit has to be at ground level, the pipes run down the back of the house in white trunking. Our standard price includes up to 5 m of pipe, so a three-storey drop costs more, and we price it in your quote. On some models, runs over 10 m also need extra refrigerant, which we include.
The drain carries away the water the unit takes out of the air. A high wall unit in a loft can almost always drain by gravity, to a gutter, a hopper or a gully. A floor console, or a route that has to rise, needs a small condensate pump. Pumps work well, but they make a faint hum and need checking at each service, so we avoid them when we can.
Where the outdoor unit goes
The best spot is close to the loft, out of sight from the street and away from bedroom windows, yours and the neighbours'.
- Dormer flat roof: short pipe run and out of sight. The unit sits on a frame or feet that protect the roof covering
- Rear wall at loft level: on a bracket, reached with an access tower if needed. We quote for access
- Ground level at the back: easy to service, but a longer pipe run down the house
- Mansard flat top: often tucked out of view behind the parapet
Timing it with your loft builder
Plan early
Tell your builder or architect you want air conditioning. We agree unit positions, the outdoor unit and the pipe route from the drawings or a site visit.
Electrics
Ask your builder's electrician to add a fused spur for each indoor unit at first fix. It's cheaper now than after the walls are finished.
First fix
While the studs and joists are open, we run the refrigerant pipes, drain and cable inside the walls or floor. We pressure test them and cap the ends.
Board and decorate
Your builder plasterboards, skims and decorates. The capped pipe ends stay marked where the units will go.
Second fix
We hang the indoor unit, fit the outdoor unit, connect, vacuum and commission the system, then show you how to use it.
Loft air conditioning prices
Most lofts need a 3.5 kW or 5 kW unit. All
- from£2,050inc. VAT
A living room
3.5 kW wall unit
- from£2,450inc. VAT
Open plan or a loft
5 kW wall unit
- from£2,350inc. VAT
Floor-standing unit
2.5 kW console
- from£3,650inc. VAT
Two rooms, one outdoor unit
Multi-split
- from£4,950inc. VAT
Ducted, per zone
Hidden in the ceiling, survey needed
Loft air conditioning questions
Can you fit air conditioning in a loft with sloped ceilings?
Yes. A wall unit goes on the gable, party wall or dormer wall if there's enough height. If there isn't, a floor console sits on a low wall instead. If there's a deep enough void, a ducted unit can hide in the eaves with only grilles showing.
What size air conditioning unit do I need for my loft?
Most loft bedrooms need 3.5 kW, and large or very glazed lofts need 5 kW. A small loft room with one or two roof windows may manage with 2.5 kW. We size it properly at the survey from the floor area, glazing and which way the roof faces.
When should air conditioning go in during a loft conversion?
Plan it before the build starts, and fit the pipework at first fix, while the walls and floor are open. The units go on at second fix, after decorating. That way no pipes or trunking show.
Where does the water go?
Through a small drain pipe that runs with the refrigerant pipes, usually by gravity to a gutter, hopper or gully. If the route has to rise, a small condensate pump lifts the water. It makes a faint hum and gets checked at each service.
Do I need planning permission for the outdoor unit?
Often not on a house, but conservation areas, listed buildings and positions facing the street usually need checks or consent. The rules for air source heat pumps, which most air conditioning units are, changed on 29 May 2025. Our planning guide explains them, and we check your address at the survey.
Will it heat the loft in winter too?
Yes. The systems we fit are reversible heat pumps, so the same unit warms the loft on cold mornings. It's an efficient way to heat a room that's often the hardest to reach from the main heating system.
How much does loft air conditioning cost?
A 3.5 kW wall unit starts from £2,050 and a 5 kW unit from £2,450, including VAT. A floor console starts from £2,350, and a two-room multi-split from £3,650. Long pipe runs, condensate pumps and access towers are priced in your quote.
Is a portable air conditioner enough for a loft?
Usually not. A portable needs its hot air hose out of a window, which is awkward with roof windows and lets warm air back in. They're also louder and much less powerful than a fixed unit sized for the room.