Office Air Conditioning: Choosing and Installing a System

Most UK offices are cooled by wall-mounted splits, ceiling cassettes, concealed ducted units or a VRF system, chosen by layout and number of zones. Cooling is not ventilation, a system over 12kW needs a TM44 inspection every five years, and F-Gas leak checks follow the refrigerant charge.

Picture an office manager in the first hot week of the year, with a south-facing floor where the desks nearest the windows are unusable by two in the afternoon, a pedestal fan on every third desk, and a landlord who has said yes in principle. What nobody has settled is whether the answer is one big system or four small ones, and who looks after it afterwards. This guide is written for that person.

At a glance

Question	Answer, with the rule behind it
Small office, one or two rooms	Daikin describes its Sky Air range as "ideal for smaller spaces, with separate controls for each unit"
Several zones or floors	Daikin positions VRV for medium-sized office buildings, with units controlled "centrally or individually"
Does the air conditioning ventilate the office?	No. Approved Document F asks for outdoor air at 10 litres per second per person or 1 litre per second per m2, whichever is higher
Inspection of the system	TM44: systems over 12kW effective rated output, inspected no more than five years apart
F-Gas leak checks	From 5 tonnes CO2 equivalent: every 12 months, or every 6 months from 50 tonnes
New single split with an old refrigerant	Banned from 2025 where it holds less than 3kg and the GWP is above 750

Source: GOV.UK, a guide to air conditioning inspections and GOV.UK, checking F gas equipment for leaks. The Daikin quotes are from the pages linked below, and the ventilation and ban rows are sourced in the sections that follow.

Which system suits which office

Choosing a system is mostly a question of how many separate spaces you have and how much you can disturb the ceiling. A single room that overheats needs one unit and one thermostat. A floor of cellular offices, a boardroom and an open-plan area that all get hot at different times wants zoning, so that someone sitting in one corner is not paying to cool an empty meeting room. We go through the engineering side of the first choice in our guide to split and cassette air conditioning, and the multi-zone end is covered in the VRF air conditioning guide.

System type	Typical office layout it suits	Typical installation impact	What the manufacturer says (Daikin)
Wall-mounted split	Small offices, meeting rooms, a single hot room	Lightest. Indoor unit on a wall, outdoor unit outside, pipework between	Sky Air is "ideal for smaller spaces, with separate controls for each unit"
Ceiling cassette	Open-plan areas and larger rooms	Needs a ceiling void and tile cutting, so more disruption than a wall unit	Cassettes are "engineered to provide optimal air flow in all types of small and large spaces"
Concealed (ducted) ceiling unit	Offices with a finished suspended ceiling and a wish to see no hardware	Ceiling void work plus grilles. Neatest result	Concealed ceiling units are "ideal for all types of interiors"
VRF or VRV	Several zones or floors with different loads	Larger scheme: one or more outdoor units serving many indoor units	VRV is aimed at medium-sized office buildings, with options "to control your units centrally or individually"
VRV heat recovery	Offices where some rooms need cooling while others need heat	As VRF, with extra pipework for the heat recovery design	VRV 5 Heat Recovery offers "simultaneous cooling and heating", with a "3-pipe heat recovery design"

Source: Daikin UK, offices and large buildings and Daikin UK, VRV. The installation impact column is our own engineering view and is not a manufacturer figure.

Those are Daikin's own descriptions, quoted to show how a manufacturer positions each type, not as a recommendation of a brand. The right choice for your floor depends on the survey rather than the catalogue. Large buildings sit above all this. Daikin's offices page lists chillers and air-side equipment as the optimal solution for large office buildings, which is a different kind of project.

We are deliberately not giving a kW-per-square-metre rule of thumb here. Heat gain from people, computers, lighting, glazing and orientation varies too much, and an engineer who sizes a system from floor area alone is guessing. A proper survey looks at all of it.

Air conditioning is not ventilation

This one catches office managers out. A cooling unit takes warm air from the room, cools it and puts it back. Whether the office also gets fresh air is a separate matter, and in England it is governed by Part F of the Building Regulations. Approved Document F, Volume 2 (the 2021 edition, taking effect on 15 June 2022 for use in England) says that for offices "outdoor air should be supplied for occupiable rooms" at whichever of these gives the higher total: 10 litres per second per person, or 1 litre per second per m2 of floor area (Approved Document F, Volume 2, paragraph 1.32).

The same document asks for common spaces such as corridors and lift lobbies to have either natural ventilation openings of at least 1/50 of the floor area, or mechanical supply of 0.5 litres per second per m2. For ventilation systems that recirculate air between rooms, it also asks that they can operate in a mode that reduces the risk of airborne infection, for example by running on 100% outdoor air, with UV-C or HEPA options as alternatives (paragraph 1.37). A basic split that only recirculates the room's own air does none of this by itself, which is why a freshly cooled office can still feel stuffy. Whether your building meets the document is a question for a ventilation designer or building control, not something an air conditioning quote answers.

The law on how hot an office may get sits in a different place. The Workplace (Health, Safety and Welfare) Regulations 1992 require a "reasonable" temperature in indoor workplaces during working hours, with no fixed upper figure, and we cover what that means in practice in our piece on workplace temperature law in the UK.

The duties that come with an office system

Installing the system is the start of it. Once it is running, a handful of obligations attach to whoever operates it, and they are worth knowing before you sign, because they affect who you ask to maintain it. The table sets out the main ones.

Duty	Trigger	Frequency or rule	Where it comes from
F-Gas leak check, smaller band	F gas equivalent to 5 to less than 50 tonnes CO2	"At least once every 12 months"	GOV.UK leak checks guidance
F-Gas leak check, middle band	50 to less than 500 tonnes CO2	"At least once every 6 months"	GOV.UK leak checks guidance
Automatic leak detection	500 tonnes or more	"You must fit a leak detection system", and with one fitted the gap between checks can be doubled	GOV.UK leak checks guidance
Hermetically sealed systems	Below 10 tonnes CO2	No maximum period between leak checks	GOV.UK leak checks guidance
F-Gas records	Equipment holding 5 tonnes CO2 or more	"You must keep records for 5 years", including gas added and the dates and results of leak checks	GOV.UK record F gas guidance
TM44 air conditioning inspection	Effective rated output of more than 12kW, or several units whose combined output is more than 12kW	Inspected by an energy assessor, intervals "no more than five years apart", first inspection within five years of first being put into service	GOV.UK guide to air conditioning inspections
Ventilation	Office building work in England (2021 edition, from 15 June 2022)	10 litres per second per person or 1 litre per second per m2, whichever is higher	Approved Document F, Volume 2, paragraph 1.32

Source: GOV.UK, checking F gas equipment for leaks and GOV.UK, record F gas in equipment you own or service. The TM44 row is from the GOV.UK air conditioning inspections guide and the ventilation row from Approved Document F, both linked above.

To put the bands in context, the leak checks page gives 2.4kg of R-410A as the 5 tonne point in its frequency table. The bigger the scheme, the more likely the charge crosses a band. The page also says responsibility is shared between the users of equipment and the technicians who install and maintain it, and that leaks should be repaired as soon as possible with a repeat test within a month. If you want the full TM44 picture, our TM44 inspection guide goes through it.

What the single split ban means for a new install

Since the start of 2025 a particular combination has been off the market in Great Britain. The gov.uk bans guidance lists "single split" systems that contain less than 3kg of refrigerant, defined as "a system with one cooling coil connected to a remote condensing unit", with a GWP above 750, from 2025. Exempt categories listed include larger air-conditioning or heat pump systems, such as chillers or larger split systems. The page was last updated on 27 August 2026 (GOV.UK, bans on F gas in new products and equipment).

For an office, that means a new small single split has to use a refrigerant at or below that threshold. On gov.uk's own list of F gases, HFC-32 has a GWP of 675 and R-410A has 2088, so on those figures a new R-410A single split would fall on the wrong side of the line and an R-32 one would not. Read the refrigerant named on any quote for a new single split with that in mind. Whether a particular multi-room or VRF scheme counts as a single split under the definition is a question to put to your installer, because the exemption wording for larger split systems is the part that needs reading carefully.

Planning, outdoor units and the landlord

Outdoor units need somewhere to go, and in a leased office that usually means the landlord's permission long before the council's. Whether you need planning permission depends on the building and where the unit sits, and our post on planning permission for air conditioning covers it. Ask the landlord early about roof space, riser routes for pipework and condensate drainage, because those details can hold up an office install as much as the equipment can.

Running costs are the other conversation to have before you order. Our guide to air conditioning running costs in the UK looks at what drives the bill without quoting anyone's tariff.

When to call an installer

If you are looking at a floor with several zones, a ceiling you do not want to see, or a landlord who needs convincing, get an engineer in to survey it rather than working from a catalogue. Be Cool is a family-run London firm, trading since 2004, with F-Gas certified engineers and more than 2,000 projects behind us, and we install across London and the South East. Our page on commercial air conditioning installation in London explains how we approach an office job.

Frequently asked questions

What type of air conditioning is best for a small office?

For one or two rooms, a wall-mounted split is the usual starting point, and Daikin describes its Sky Air range as ideal for smaller spaces with separate controls for each unit. A survey will confirm it.

Does office air conditioning bring in fresh air?

Not by itself. Approved Document F separately asks for outdoor air at 10 litres per second per person or 1 litre per second per m2, whichever is higher, in office building work in England.

Does my office air conditioning need a TM44 inspection?

If the effective rated output is more than 12kW, or several units add up to more than 12kW, yes. Inspections must be no more than five years apart and done by an accredited energy assessor.

How often must the refrigerant be leak checked?

At least once every 12 months for 5 to less than 50 tonnes CO2 equivalent, and every 6 months from 50 tonnes. Hermetically sealed systems below 10 tonnes have no maximum period.

Can I still fit a new single split with R-410A?

Not if it holds less than 3kg, because the ban on single splits above a GWP of 750 has applied from 2025. R-410A is 2088 on gov.uk's list, so check the refrigerant on your quote.

Before you order

The equipment is the easy part of an office job. The decisions that matter are zoning, where the outdoor units go, how fresh air arrives and who services the system afterwards. Get those settled before anyone prices a unit, and the quote you receive is one you can compare properly.

About the author: Ali Elm runs Be Cool Refrigeration & Air Conditioning, a family-run London firm that has been installing, servicing and repairing commercial refrigeration and air conditioning since 2004. His F-Gas certified team has delivered more than 2,000 projects across London and the South East.

Last updated: 23 October 2026