Office air conditioning
By Airva Editorial Team · Checked against published UK guidance · Updated
Every office has the same argument. One end of the floor is too cold, the other is too warm, and someone has taped over the thermostat. It is almost never an equipment fault, and it is almost never solved by buying more capacity. It is a zoning failure — two areas with genuinely different thermal profiles sharing one control, so whichever way it is set, half the floor is wrong.
Getting an office right is mostly about matching zones to how the space actually behaves, and counting a load that has changed considerably in the last decade.
The thermostat war is a design problem
A single open-plan floor is not one thermal environment. Within it:
- The south and west perimeter takes solar gain through the afternoon. The north side does not.
- The core has no external gain at all but concentrates people and equipment.
- Meeting rooms go from empty to eight people in a minute, then back.
- The desk under the supply grille is a different climate from the desk six metres away.
Put all of that on one zone and you have guaranteed complaints. Zoning to match — perimeter separate from core, meeting rooms on their own control, and a separate zone for any server or comms room — costs more in dampers, indoor units and controls, and it is the difference between a system people stop noticing and one they fight.
The load has changed, in both directions
Two shifts have moved office cooling loads since most existing systems were designed:
Equipment loads fell. Banks of desktop PCs and CRT monitors gave way to laptops and flat panels. Many older office systems are now meaningfully oversized for the equipment actually in the room — which sounds like good news and is not. Oversized systems short-cycle, control humidity poorly, and leave rooms feeling clammy at the set temperature.
Occupancy became volatile. Hybrid working means a floor designed for 100 people might hold 30 on Monday and 90 on Wednesday. A system sized and controlled for full occupancy every day wastes a great deal of energy; one sized for the average fails on the busy days.
The design answer to volatility is not more capacity, it is better control: zoning, scheduling, and setback rather than off. Our energy efficiency guide covers where the savings actually sit.
What the law requires, and what it does not
There is no maximum legal working temperature in the UK. HSE is explicit that no meaningful upper limit can be imposed, because in many workplaces high temperatures are created by the work itself [1]. What employers must do is keep the temperature at a comfortable level and provide clean, fresh air [1]. The minimum for an indoor workplace is normally at least 16°C, or 13°C where much of the work involves rigorous physical effort [1] — the former being the relevant figure for desk work.
So "the office must be below 30°C" is not a rule. The duty is to keep conditions reasonable, and in a modern glazed office building that duty is difficult to discharge in July without cooling.
Note also that comfort cooling recirculates room air. It does not ventilate. The clean fresh air part of the duty [1] is a separate provision and should be assessed on its own terms.
Which system suits which office
| Space | Typical answer | Notes |
|---|---|---|
| Open-plan floor with suspended ceiling | Ceiling cassettes | Four-way throw covers open areas evenly; needs the void |
| Multi-floor building | Multi-zone VRF | Independent control per zone from shared plant |
| Cellular offices | Wall units or small cassettes per room | Simple, and each room gets its own control |
| Meeting rooms | Own zone, sized for full occupancy | The classic under-sizing failure: sized for the average, used at peak |
| Server or comms room | Separate dedicated system | Runs when the office is closed — see server rooms |
| Reception with street doors | Own zone | Door openings and glazing make it a different problem from the core |
Noise, and the open-plan problem
Office acoustics are already contested territory. A cassette or ducted unit running at high fan speed adds a broadband hum that raises the background level across a whole floor — which some people find helps with speech privacy and others find exhausting.
Specify on low-speed sound data, size so the system spends most of its time there, and pay attention to the units above meeting rooms, where the difference between quiet and intrusive decides whether a room is usable for calls.
Planning: usually required
Offices do not get the permitted development right householders have. Part 14 provides non-domestic classes for solar, ground source and water source heat pumps, but none for air source [2]. An external condenser on an office building will generally need a planning application, and the narrow industrial-land exception in Part 7 does not apply to office use.
Plan for it as a programme item. Our planning and compliance guide sets out the position.
The duties that follow
F-gas leak checks. Responsibility sits with the party using the equipment, with records kept five years [3]. Intervals follow refrigerant charge, starting at least every 12 months from 5 tonnes of CO₂ equivalent — which for R-410A is 2.4kg [3]. A multi-zone office system clears that easily.
TM44 inspections. Above 12kW combined effective rated output, inspection by an accredited energy assessor at intervals not exceeding five years [4]. The threshold aggregates across the units serving a building under one person's control, so several modest cassettes count together. See our TM44 and F-gas guide.
Who carries them in a let building is a lease question rather than an occupation question — see the landlord guide.
What office air conditioning costs
Priced from a survey, because zone count and plant access drive it more than floor area. As planning figures: ceiling cassettes typically £2,500–£4,500 each installed, and a multi-zone VRF serving a floor or a small building commonly £8,000–£20,000 depending on zone count and plant siting. Our commercial cost guide covers the hidden lines, including planning, out-of-hours working and recurring compliance.
Frequently asked questions
Is there a maximum legal office temperature in the UK? No. HSE states no meaningful upper limit can be imposed. Employers must keep the temperature at a comfortable level and provide clean, fresh air [1].
What is the minimum office temperature? Normally at least 16°C for an indoor workplace, or 13°C where much of the work involves rigorous physical effort [1].
Why is one side of our office always wrong? Almost always zoning. Perimeter and core, and different elevations, have genuinely different loads. If they share one control, one of them will be wrong whatever the setting.
Do we need planning permission? For an external unit on an office, generally yes — there is no non-domestic permitted development class for air source heat pumps [2].
Does air conditioning ventilate the office? No. Comfort cooling recirculates room air. Fresh-air ventilation is a separate provision.
Our system is old — is it oversized? Quite possibly, if it predates the shift from desktops to laptops. Oversizing shows up as short-cycling and a clammy feel at the right temperature.
Get an office design that matches the building
Tell us about the premises — floor area, layout, ceiling type, occupancy pattern and orientation — and we will match you with one vetted, commercially capable installer who will zone it properly: start a business enquiry.