09th Aug, 2019 Read time 5 minutes

Thermal comfort in the workplace: is it too hot to work?

Across the UK, temperatures have been soaring lately, leaving many office staff praying for a few days of cooler weather. Many dread going into offices which lack air conditioning and feel stuffy on entry.

There’s no law for maximum working temperature, or when it’s too hot to work. However, in offices or similar environments, the temperature in workplaces must be reasonable and employers must still stick to health and safety laws.

This includes keeping the temperature at a comfortable level, which is known as thermal comfort, and providing clean and fresh air.

There are six basic factors which usually cause discomfort. Employees should talk to their employer if the workplace temperature isn’t comfortable.


Six Basic Factors

The six factors affecting thermal comfort which are environmental and personal. These factors may be independent of each other, but together contribute to an employee’s thermal comfort.

The most commonly used indicator of thermal comfort is air temperature – it is easy to use and most people can relate to it. However, air temperature alone is not a valid or accurate indicator of thermal comfort or thermal stress. It should always be considered in relation to other environmental and personal factors.


Air temperature

This is the temperature of the air surrounding the body. It is usually given in degrees Celsius (°C).


Radiant temperature

Thermal radiation is the heat that radiates from a warm object. Radiant heat may be present if there are heat sources in an environment.

Radiant temperature has a greater influence than air temperature on how we lose or gain heat to the environment.

Examples of radiant heat sources include: the sun, fire, electric fires, ovens, kiln walls, cookers, dryers, hot surfaces and machinery, molten metals etc.


Air velocity

This describes the speed of air moving across the employee. Air velocity is an important factor in thermal comfort and may help cool down if the air is cooler than the environment.

Using air conditioning, fans, or even a breeze from open windows can help to cool staff down.



Relative humidity is the ratio between the actual amount of water vapour in the air and the maximum amount of water vapour that the air can hold at that air temperature.

High humidity environments have a lot of vapour in the air, which prevents the evaporation of sweat from the skin and can prevent people from being able to cool down.

Relative humidity between 40% and 70% does not have a major impact on thermal comfort, but in some cases, the relative humidity may be higher than 70% and this can begin to cause thermal discomfort. Humidity in indoor environments can vary greatly depending on the industry, the equipment used, and the necessary clothing that needs to be warm.


Clothing insulation

Wearing too much clothing or personal protective equipment (PPE) may be a primary cause of heat stress even if the environment is not considered warm or hot. If clothing does not provide enough insulation, the wearer may be at risk from cold injuries such as frostbite or hypothermia in cold conditions.

Clothing can be a cause of thermal discomfort, but can also act as a control method for adapting to the climate we are working in. For example, you can add layers of clothing if you feel cold, or remove layers of clothing if you feel warm.


Work rate/metabolic heat

The more physical work we do, the more heat we produce. The more heat we produce, the more heat needs to be lost so we don’t overheat. The impact of metabolic rate on thermal comfort is critical.

A person’s physical characteristics should always be borne in mind when considering their thermal comfort, as factors such as their size and weight, age, fitness level and sex can all have an impact on how they feel, even if other factors such as air temperature, humidity and air velocity are all constant.


What employees can do:

  • Add or remove layers of clothing depending on how hot or cold you are
  • Use a desk or pedestal fan to increase air movement
  • Use window blinds (if available)
  • In warm situations, drink plenty of water
  • If possible, work away from direct sunlight or sources of radiant heat
  • Take regular breaks to cool down in warm situations and heat up in cold situations

What employers can consider:

  • where possible ensuring windows that open, fans are provided to promote local cooling and radiators can be switched off or air conditioning units are maintained
  • introducing work systems to limit exposure, such as flexible hours or early/late starts to help avoid the worst effects of working in high temperatures
  • relaxing formal dress codes
  • insulating hot plant or pipes
  • moving workstations away from hot plant or out of direct sunlight
  • including assessments of thermal risk as part of workplace risk assessments


Jobs that involve extreme temperatures

In some workplaces, extreme temperatures are not seasonal but are created by the work, like in some manufacturing processes. These temperatures can lead to serious health effects if not managed effectively.

You should seek specific advice on temperature if you are working in very high or low temperatures, for example on heat stress, dehydration or cold stress.


If you feel that your workplace isn’t following the advice above to ensure a comfortable thermal comfort is reached, then you should raise the issue with senior members of staff. Alternatively, get in touch with your union or other workplace representatives to escalate the issue and gain more advice.

Brands who we work with

Sign up to our newsletter
Keep up to date with all HSE news and thought leadership interviews