Temperature at Work - What is thermal comfort and how do i measure it?

If you’ve found your way to this article, you’re most likely uncomfortable with your working conditions, or maybe you’re a considerate employer ensuring you are doing everything you need to provide your staff with reasonable working conditions. Either way, the questions remain the same….

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The answers to all these questions can be found with the Health and Safety Executive (HSE), and more specifically the Workplace (Health, Safety and Welfare) Regulations 1992, but that’s long and boring and filled with jargon. So here is our quick version.

Disclaimer: This is intended for a UK target audience as the legal regulations discussed derived from UK legislation which could differ significantly from other countries.

Legal Workplace Temperature

The Workplace (Health, Safety, and Welfare) Regulations 1992 place a legal responsibility on all employers to provide a ‘reasonable’ workplace temperature. The good news is that they are obligated to prove they are taking reasonable steps to provide a suitable environment. Unfortunately, reasonable is open to interpretation and can vary significantly depending on the job role, types of tasks expected, and equipment and clothing worn.

My workplace is too warm

Unfortunately, there is no legally defined upper temperature for any type of workplace. This is largely due to existence of workplaces such as bakeries and foundries where it is expected that the temperature will significantly climb. In these environments, risk assessments are mandatory, and employees must show a conscious effort to measure heat levels, risk and make reasonable efforts to reduce the heat.

If you’re in an office or similar and you believe your workplace is too warm, keep reading, you need to know about ‘Thermal Comfort’ and we explain it below.

My workplace is too cold

The good news is that there are suggested ‘reasonable’ minimum temperatures provided by the HSE. The Approved Code of Practice suggests the minimum temperature in a workplace should be at least 16°C. If the work involves rigorous physical effort, the temperature should be at least 13 degrees Celsius. However, the bad news is that these are not absolute legal requirements; the employer has a duty to determine what reasonable comfort will be in the circumstances.

I know what you’re thinking, 16°C seems a little chilly right? ‘Thermal Comfort’ comes into the picture again and is a little more complex than the temperature of the room. Let’s take a look.

Thermal Comfort

Thermal Comfort refers to the state of mind of a person, and if they feel to hot or too cold regardless of the room temperature. It takes into account more than the simple temperature and is made up of 4 environmental factors and 2 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 and may help cool them if the air is cooler than the environment.

Air velocity is an important factor in thermal comfort for example:

  • still or stagnant air in indoor environments that are artificially heated may cause people to feel stuffy. It may also lead to a build-up in odour
  • moving air in warm or humid conditions can increase heat loss through convection without any change in air temperature
  • physical activity also increases air movement, so air velocity may be corrected to account for a person's level of physical activity
  • small air movements in cool or cold environments may be perceived as a draught as people are particularly sensitive to these movements


If water is heated and it evaporates to the surrounding environment, the resulting amount of water in the air will provide humidity. 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.

Relative humidity between 40% and 70% does not have a major impact on thermal comfort. In workplaces which are not air conditioned, or where the weather conditions outdoors may influence the indoor thermal environment, relative humidity may be higher than 70%.

High humidity environments have a lot of vapour in the air, which prevents the evaporation of sweat from the skin. In hot environments, humidity is important because less sweat evaporates when humidity is high (80%+). The evaporation of sweat is the main method of heat reduction.

When non-breathable vapour-impermeable personal protective equipment (PPE) is worn, the humidity inside the garment increases as the wearer sweats because the sweat cannot evaporate. If an employee is wearing this type of PPE (eg asbestos or chemical protection suits etc) the humidity within the PPE will be high.

How to measure Thermal Comfort

If you want to prove whether or not your working conditions are reasonable, ideally you need to begin by assessing the thermal comfort and performing a risk assessment. Ideally, this means you need to measure Temperature, Humidity and ideally Airflow. There are a few options at your disposal depending on the depth/seriousness of your problem.

All-in-one Environment Meters

Offering measurement of a combination of Temperature, Humidity, Airflow, Light and Sound in a single unit, these units are fantastic for checking thermal comfort as well as a selection of other workplace health and safety concerns such as lighting levels at work stations, noise levels from machinery and fire alarm loudness. The only downside is that this is typically a more expensive solution, but it is incredibly practical.

Individual Environment Meters

Individual environment meters offer a cheaper method of gaining an indication of thermal comfort. With these you can focus on one or two key contributing factors you feel most relevant to your particular setup, be that temperature and humidity, or temperature and air velocity.

Next Steps....

If you can demonstrate with a simple to use affordable instrument that any of the contributing factors to thermal comfort are in or outside reasonable levels, you have the legal grounding to request change or as an employer, show you have taken all reasonable steps to ensuring thermal comfort. Once you have identified thermal comfort the HSE provide recommended steps to addressing thermal comfort.