Does air conditioning make an office more productive?

Yes, once the office gets warm. Research on office work finds people perform best at around 22°C, and that performance starts to fall once the room climbs above about 23 to 24°C. A south facing office in a British summer passes that point most afternoons, and a packed meeting room passes it by eleven in the morning.

The study most often quoted on this is a review of office studies by researchers at Helsinki University of Technology and Lawrence Berkeley National Laboratory, Seppänen, Fisk and Lei (2006). It pulled together measured performance on real office tasks, such as typing, calculations and call handling times, and found the peak at around 22°C.

What temperature should an office be?

There's no legal maximum in the UK. The Health and Safety Executive asks employers to keep workplaces at a reasonable temperature, with a suggested minimum of about 16°C, or about 13°C where the work is physically demanding. Above that, it's down to the employer to assess the risk.

In practice, 21 to 23°C suits most offices. The harder part is holding it, because an office rarely gets hot evenly.

Why does an office overheat?

Four things, and most offices have at least two of them:

• Glass. A south or west facing wall of windows can put one side of a floor several degrees above the other, and the gap moves through the day.
• People. Everyone in the room gives off heat. A meeting room with twelve people and the door shut climbs fast, which is why meeting rooms are the most common complaint.
• Equipment. Computers, screens, printers and a comms cupboard running all day add up, particularly in a small office.
• The building. Top floors, flat roofs and offices above a kitchen or a shop with its heating on all take on heat from outside the room.

A single thermostat for the whole floor can't fix that, because the warm side and the cool side need different things at the same time. That's what zoning is for, and the office air conditioning page explains how a floor is split up.

Is the problem heat, or stale air?

Often both, and they're easy to confuse. A busy room with poor ventilation builds up carbon dioxide, and people describe it as stuffy, heavy or tiring even when the temperature is fine. Cooling recirculates the air in the room, so it fixes the heat but not the staleness.

If the complaint is that a room feels airless rather than hot, the answer is fresh air, and ventilation with heat recovery brings it in without throwing away the heat in winter. Many offices need a bit of both.

Does the cost add up?

For most offices, comfortably. Take an employee costing £30,000 a year. Over a normal working year that's roughly £15 an hour. If a hot afternoon costs them even five minutes of every hour, that's over £1 an hour, for each person in the room. A 3.5kW cassette holding a meeting room once it has cooled it down uses roughly the electricity of a desktop computer and a monitor, which is pence an hour.

That sum is an illustration rather than a measurement, but the direction doesn't change much whatever figures you put in: staff cost a great deal more than the electricity.

The installed price for a single ceiling cassette is £2,450, and a four cassette system for an open plan floor is around £8,500. The cost guide has the full list, including servicing.

What about the comms room?

Treat it separately. A comms cupboard or server room runs at the same load every hour of the year, including winter, and an ordinary office unit isn't built for that. It needs its own cooling and usually an alarm, which the server room cooling page covers.

Are there rules for office air conditioning?

Two that catch businesses out. A building with air conditioning over 12kW of effective rated output needs a TM44 inspection at least every five years, and four 3.5kW cassettes already cross that line. Systems holding 5 tonnes of CO2 equivalent of refrigerant or more need regular leak checks, which a typical office VRF system usually does. The commercial page sets out both.

If one room is the problem, start there. A single cassette in the meeting room that fills up after lunch is often the cheapest fix, and a free survey will tell you whether the rest of the floor needs it too.