Choosing Air Conditioning for a Small Office in South West London

Start with the building, not the brochure

Before comparing systems, check three things. First, do you own the premises or lease them? Most commercial leases require written landlord consent (often a formal licence to alter) before anything is fixed to an external wall or roof, and this can take several weeks.

Second, where can the outdoor unit sit? A rear yard, flat roof or lightwell is usually easiest. Front elevations onto the street are rarely acceptable, particularly in the many conservation areas across Fulham, Chelsea, Putney, Barnes and Wandsworth.

Third, what is the electrical supply like? Most small systems run happily on a standard single phase supply, but an older consumer unit may need a spare way or an upgrade.

Which type of system suits a small office

For most offices under about 100 square metres, the choice comes down to a handful of options. All modern systems are heat pumps, so they heat as well as cool, which can let you retire electric panel heaters.

• Single split, wall mounted: one indoor unit, one outdoor unit. The simplest and cheapest option for a single open plan room of up to roughly 40 to 50 square metres.
• Multi-split: one outdoor unit serving two to five indoor units. Good when you have a main office plus a meeting room or two, and only space for one outdoor unit.
• Ceiling cassette: sits flush in a suspended ceiling and spreads air in four directions. Tidy and even, but you need a ceiling void of around 250 to 300mm.
• Ducted: hidden entirely above the ceiling with only grilles showing. The neatest finish, with the highest installation cost and the most disruption.
• Portable units: a stopgap only. They are noisy, inefficient and need a hose out of a window.

Getting the size right

As a rough guide, offices need around 125 to 150 watts of cooling per square metre, so a 40 square metre room typically lands at 5 to 6kW. That figure climbs with large south or west facing windows, a top floor position, lots of people in a small space, or a bank of computers and printers.

Oversizing is as much of a problem as undersizing. A unit that is too large cycles on and off, creates draughts and leaves the air feeling clammy. A proper survey should include a heat load calculation rather than a guess based on floor area alone.

Server cupboards deserve separate thought. They need cooling all year round, including when the main office is in heating mode, so a small dedicated unit is usually the better answer.

What it is likely to cost

Prices depend on pipe run length, access, how the condensate drains and whether work has to happen out of hours. As a realistic guide for this part of London, a single wall mounted split usually falls between £1,800 and £3,500 installed. A multi-split serving three or four rooms tends to run from £4,500 to £9,000, and cassette or ducted systems cost more again because of the ceiling work.

Awkward access adds cost here more than in most places. Upper floor offices above shops may need scaffolding or a roof access permit, and parking restrictions and suspensions in boroughs such as Hammersmith and Fulham or Kensington and Chelsea can add to the bill. Budget for an annual service too, typically £80 to £150 per indoor unit, to keep filters clean and the warranty valid.

Planning, noise and legal points

Outdoor units on commercial premises often need planning permission, and local councils commonly ask for a noise assessment showing the unit will run well below existing background levels at the nearest neighbouring window. This matters where offices back onto flats, which is most of South West London. Quiet units, anti-vibration mounts and an acoustic enclosure usually solve it.

Any installer handling refrigerant must hold F-gas certification, so ask to see it. If the total cooling capacity in your premises exceeds 12kW, you are also required to have an air conditioning inspection (known as TM44) every five years.