Basement
air conditioning
A basement is the one room in a London house that stays cool on its own, until it becomes a kitchen, a cinema or a gym with glass doors to a lightwell. Then it is the stuffiest room in the house.
- Free survey and a fixed written price
- Sized from a calculation, not from the floor area
- One day on site for most single rooms
Accredited, and fitting the brands you know
Air conditioning we have fitted
Our own jobs, photographed on site. Real rooms, real outdoor positions, nothing from a catalogue.
Air conditioning
Outdoor unit on wall brackets
Above brick, isolator and cabling run tidy
Air conditioning
Condenser going up on straps
Lifted into a wall position, no scaffold
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Wall unit, commissioned
Set to 24 degrees and handed over
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Black wall unit in a sitting room
Chosen to sit with the room, not against it
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Ceiling cassette
Recessed flush into the ceiling
Air conditioning
Samsung Wind-Free
Cooling without a draught on the room
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Rooftop commissioning
Pressure tested and charged on gauges
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Outdoor unit at ground level
On paving beside the house, easy to service
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Black wall unit, running
Quiet enough for a bedroom
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One-way ceiling cassette
Only the grille shows
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Outdoor unit on paving
Against render, clear of the boundary
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Condenser high on a wall
On brackets where the ground was not an option
A basement room usually needs a smaller unit than the same room upstairs, 2.0 to 3.5kW, which costs 2,400 to 3,500 pounds fitted. A basement kitchen opening onto the garden is the exception and can need 7kW.
What makes a basement different is not the cooling. It is getting the pipes and the condensate out of a room that sits below the ground.
Read the full guide: 7 sections, about 3 minutes
What size a basement room needs
Using the same model as the sizing calculator on this site. Below ground the aspect and the small windows take the size down; a glass wall to the garden and a kitchen put it back up.
| Room | How it works out | Unit |
|---|---|---|
| Basement bedroom, 14 m², north, small lightwell window | 1.96, less 10% aspect, less 10% glazing | 2.0kW |
| Basement living room, 20 m², east facing | 2.80, plus 5% living use | 3.5kW |
| Basement gym, 18 m², north, one small window | 2.52, less 10% aspect, less 10% glazing, plus 5% use | 2.5kW |
| Basement kitchen diner, 25 m², south, glass doors | 3.50, plus 18% aspect, 18% glazing, 25% kitchen | 7.0kW |
Getting the water out, which is the part that goes wrong
An air conditioner takes water out of the air, several litres of it on a humid day. Upstairs it drains away by gravity; below ground there is often nowhere lower for it to fall to.
So a basement unit usually has a small condensate pump that lifts the water to a drain at ground level. The pump goes where it can be reached for servicing, and its route is decided at the survey, because a pump hidden behind a finished wall is a leak waiting to happen.
Where the outdoor unit goes
The lightwell is the obvious place and often the wrong one. A small enclosed lightwell traps the warm air the unit throws out, so it breathes its own exhaust and struggles, and the fan noise reflects straight up into the rooms above.
Better positions are usually at garden level, on the rear of the house, or on a flat roof, with the pipework taken up through the lightwell wall or a ground floor void. The longer run costs more, and it is money spent on a system that works.
Damp and humidity, not only heat
Basements are prone to damp air, and the dry mode on an air conditioner is very good at taking it out, which is often what makes a basement room feel fresh rather than cool.
What it cannot do is fix water coming through the structure. If a basement has a damp problem, that is a waterproofing job first, and we will say so rather than fit a unit over it.
Cinema rooms and gyms
A home cinema or a gym has loads the calculator does not see: a projector and amplifiers running for hours, or two people exercising. Those rooms are sized from the equipment and the use, not from the floor area, and they usually need one size up.
What it costs
| Scope | System | Installed price |
|---|---|---|
| Basement bedroom or snug | 2.0 to 3.5kW wall unit | £2,400 to £3,500 |
| Basement kitchen or open-plan room | 5.0 to 7.0kW | £2,750 to £4,400 |
| Two basement rooms on one outdoor unit | Multi-split | £4,300 to £5,800 |
| Ceiling cassette or slim ducted, concealed | Common in a new basement fit-out | Add £900 to £1,500 |
| Pipe run over 25 metres | Up to a roof or rear garden position | Add £30 per metre |
Every figure on this site is an estimate built from the quotations we issued in 2026 and our own installation experience. It is not a quotation. The price you are given after the free survey is the price you pay.
Other rooms
Bedrooms
A bedroom is the hardest room in the house to get right, and not because it is difficult to cool.
BedroomsLoft conversions
A loft conversion is reliably the hottest room in a London house, and it is hot for three reasons at once: the roof above it, the heat rising into it from the rest of the house, and insulation that was designed to keep warmth in during winter.
Loft conversionsConservatories
A conservatory is the one room where we will sometimes tell you not to buy air conditioning yet.
ConservatoriesHome offices
A home office is a small room with a person and several hundred watts of electronics in it, occupied for eight hours at exactly the time of day the sun is on the building.
Home officesGarden offices
A garden office is a small insulated box with a glass front, which is exactly why it is too hot to work in by June and too cold by November.
Garden officesSize any room
The calculator behind every figure on this page, in kW and BTU, with the working shown.
Sizing calculator
Your estimate
£2,400to£3,200
Supplied, fitted, commissioned and certificated. Includes VAT.
Send this on WhatsAppPrice it for this room
One room, so the two things that move the number are how big it is and which kind of indoor unit you want.
Last step: where do we send your written price?
Every figure on this site is an estimate built from the quotations we issued in 2026 and our own installation experience. It is not a quotation. The price you are given after the free survey is the price you pay.
Basements: common questions
Can the outdoor unit go in the lightwell?
Sometimes, if the lightwell is large and open to the sky. A small enclosed one traps the unit's warm exhaust and reflects its noise upwards, and the unit never performs as it should.
We look at the lightwell at the survey and tell you honestly whether it will work.
Where does the water from a basement unit go?
Usually up. A small condensate pump lifts it to a drain at ground level, and the pump is placed where it can be serviced.
Where there is a drain lower than the unit, gravity does the job and no pump is needed.
Will air conditioning fix a damp basement?
It will dry damp air and make the room feel fresher. It will not stop water coming through the walls or floor, which needs the waterproofing looked at first.
Fitting a unit over an active damp problem just hides it for a while.
Can the same unit heat the basement in winter?
Yes, and basements are often at the end of the heating system. The unit heats at roughly three to four units of heat per unit of electricity.
Size your own room in about a minute.
Free survey for a basement
We measure the room, do the heat load calculation properly, and give you a fixed written price with the model on it. If a smaller unit is the right answer, we will tell you.
Monday to Friday 9am to 7pm, Saturday 10am to 3pm, Sunday closed
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