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Many of us spend a significant part of our waking hours inside an office and want to feel healthy and comfortable there. If it’s too cold concentration and cognition may drop off as the body redirects energy, while overheating makes us tired and irritable.
Charlie Harris  image Charlie Harris

Health & Environment

What’s the optimal temperature for a UK office?

Many of us spend a significant part of our waking hours inside an office and want to feel healthy and comfortable there. If it’s too cold concentration and cognition may drop off as the body redirects energy, while overheating makes us tired and irritable.

What’s the optimal temperature for a UK office? 

Many of us spend a significant part of our waking hours inside an office and want to feel healthy and comfortable there. If it’s too cold concentration and cognition may drop off as the body redirects energy, while overheating makes us tired and irritable. 

Maintaining an ideal temperature in office workplaces is getting more challenging. South London recently saw its coldest January day in a decade, while last July central London experienced a record 40.2°C (104°F). The “urban heat island” effect can push the temperature up to 8°C higher in the centre of big cities.  

In a typical office set-up where a business rents a commercial space, managing the temperature within its office is one of its responsibilities as tenant (this will depend on the lease). As employers, businesses are legally obliged to keep employees safe – that includes making sure the office isn’t unacceptably cold, draughty or stuffy. 

Minimum and maximum office temperature

Actually, there’s no legal upper or lower limit. Instead, government guidance via the Health & Safety Executive (HSE) recommends at least 16°C [61°F] for workplaces like offices, but doesn’t advise a top number. 

Employers must provide a “reasonable” temperature and adequate ventilation indoors under the Workplace (Health, Safety and Welfare) Regulations 1992. But there’s no defined optimal temperature because everyone perceives “too hot” and “too cold” based on their own metabolism.

In 2015 researchers at Maastricht University found women generally preferred a warmer office than men, by up to 3°C. Such differences are why nearly 55 per cent of office workers told one survey they’d argued over temperature.

Is there an ideal temperature? 

The TUC’s take is that 22°C to 25°C is the comfort zone for productivity, but once the interior gets to 24°C employers should take action if workers feel uncomfortable. The Chartered Institution of Building Services Engineers (CIBSE) says 28°C-plus indoors for long periods will lead to increased dissatisfaction and reduced productivity.

One 2006 US study focusing on office work suggested productivity is highest when the temperature is around 22°C and decreases below 20°C and above 23–24°C.

Health and safety legislation also says employers should carry out risk assessments, manage any potential hazards relating to heat or cold and tell workers what measured they are taking. This includes consulting with workers on the best ways to cope with high or low temperatures.

Think “thermal comfort”

It’s not just air temperature that affects whether people feel too hot or cold in the office; environmental and personal factors also affect perceptions. A non-air-conditioned office may tend to feel muggy if it’s humid outside. Someone with a thyroid condition or who is pregnant, or sitting close to a heating pipe or large equipment may feel more uncomfortable.

The HSE’s downloadable checklist is a handy tool for assessing the level of thermal comfort in an office using six indicators: air temperature, air speed and movement, humidity, radiant temperature from a heat source, and people’s metabolism and clothing.

It advises using the checklist to ask workers for feedback around each indicator. If this process identifies a problem, it also suggests steps relating to the environment, people’s behaviour, and training and information. The Chartered Institution of Building Services Engineers (CIBSE) also offers practical tips.

Provide personal control

Letting people adjust their own level of comfort can be as straightforward as relaxing a formal office dress code during a heatwave and providing a cold water dispenser or hot drinks machine. With sustainability in mind, water coolers that use a fixed supply create less landfill waste and transportation emissions than standard refillable ones, according to University of Pittsburgh researchers.

Offering portable heaters, desk fans and air conditioners is another option. The CIBSE says air movement is an important control: simply using a fan to increase it can have the same effect as turning the thermostat down by 2°C.

Use natural ventilation 

A cost-free tool for moderating temperature, get more fresh air circulating inside the office by checking that air vents and trickle vents on windows are open, and opening windows and doors (fire doors must be kept shut). In older buildings, windows may have been painted shut. Regular cleaning of key elements like vents and air ducts is essential

If people are saying a meeting room is too warm, HSE recommends opening all the doors and windows during breaks – even 10 minutes an hour can help. 

Look at windows
In many modern highly insulated offices with fixed windows the building retains heat to meet energy efficiency targets, which can lead to overheating in summer. Fitting blinds can reduce heat gain and glare, but at the cost of natural light and visibility. Alternatively, thin window films can reduce passive heat gain from solar radiation and can be fitted inside or outside. 

An Italian study of one office building with over 1,000sqm of windows found that exterior film managed to lower the temperature inside by up to 5°C even though the aircon was switched off.

Manufacturer 3M provides a useful guide to choosing the most suitable solar film. For example, the higher the TSER (total solar energy rejected) rating, the less heat is transmitted into the office. A higher U-value indicates better resistance to heat loss, which can keep the interior warmer in winter.

Adapt the space

If a significant number of people are still uncomfortable, businesses may need to make further changes like moving workstations further apart, or away from heat sources, reducing heat gain by installing low-energy lights, and insulating heat sources like pipes. 

The HSE says engineering controls are a key consideration. This could mean installing large ceiling fans to boost air movement in bigger offices or bigger air conditioning units to cope with higher air temperatures and humidity. Draughts, smells and stuffiness can indicate poor ventilation. CO2 (carbon dioxide) monitors can help identify the specific source. The HSE has advice on using these in different office spaces.

Smarter controls

Rather than a control that individuals can keep adjusting, modern HVAC (heating, ventilation and air conditioning) systems can include programmable thermostats. And smart sensors can constantly monitor conditions including air temperature, humidity and CO2. These can make the office more comfortable and improve energy efficiency. 

For instance, Pressac says its wireless and solar-powered CO2 sensors are easy to fit. These were used in a large multi-business office block in Paddington where the ventilation system was running at full speed all day. The sensors let it respond to the actual number of people in the office (and varying CO2 levels).

It’s also essential to set up a regular maintenance schedule for HVAC systems. A ventilation engineer can check the settings and whether working as designed. The Building Engineering Services Association has a list of accredited members.

Get professional advice

Going further, an independent review by a specialist consultant could identify how to achieve optimal thermal comfort. Assurity Consulting, for instance, says its service covers workplace humidity, temperature and airflow but also measures the levels of specific gases like CO2.

Refurbishment and maintenance specialist TPG says a typical situation is where a business with a mix of open-plan office, enclosed meeting rooms, a mid-range HVAC system set to automatically stay at 21°C, and workers who report feeling both too hot and too cold. It could be that individual units are “fighting” each other, creating temperature swings.

It suggests establishing a temperature “rule” of 19°C to 23°C and using heat-only and cool- only settings. For example, in colder months the system could be timed to come on before the office opens and off mid-morning, as body and equipment heat builds up.

Manage expectations 

A minority of workers will probably always be more sensitive to temperature. Deciding on the optimal temperature range, clearly communicating it to workers, and encouraging them to report if they’re feeling uncomfortable, helps them to understand the issues involved and that their employer values their comfort.

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