Short answer. UK law requires a reasonable workplace temperature and sets no maximum. The Approved Code of Practice suggests at least 16°C for most indoor work and 13°C where the work involves severe physical effort, but those are guidance figures, not statutory minimums. The duty is to manage heat and cold as a health and safety risk, whatever the thermometer says.
Every summer, the same question does the rounds in offices, warehouses and factories: is it too hot to work? Staff search for a maximum workplace temperature and share posts claiming it is illegal to work above a certain figure. There is no such figure in UK law. That does not mean employers have no obligations when the temperature climbs.
The Workplace (Health, Safety and Welfare) Regulations 1992 require the temperature in indoor workplaces to be "reasonable" during working hours. Regulation 7 and the accompanying Approved Code of Practice, L24 (Workplace health, safety and welfare), suggest a working minimum of 16°C for most indoor work and 13°C where the work involves severe physical effort. Those figures sit in the ACOP rather than in the regulations themselves, so they are guidance on what "reasonable" normally looks like, not a statutory floor. In practice they are what an inspector will measure you against.
There is no maximum temperature set out in law. L24 does not fix an upper limit, largely because what feels tolerable depends on humidity, air movement, the work being done and what people are wearing, and not solely on the reading on a thermometer. That gap is often reported online as meaning employers have no duty at all once it gets hot. That is not correct.
There is no single legal working temperature that applies in every workplace, hot or cold. What the law requires instead is a "reasonable" temperature, judged against the general duty under the Health and Safety at Work etc. Act 1974 to protect employees' health, safety and welfare so far as is reasonably practicable, and the duty under the Management of Health and Safety at Work Regulations 1999 to assess foreseeable risks. In a UK summer, heat is a foreseeable risk, and it should be assessed and managed like any other hazard rather than left until someone complains.
Heat stress occurs when the body cannot cool itself effectively. Symptoms range from mild discomfort, fatigue and reduced concentration to heat exhaustion, heat stroke and collapse; heat stroke can be fatal if it is not recognised and treated quickly.
Risk depends on more than air temperature alone. Humidity, radiant heat from sun exposure, ovens or industrial processes, air movement, workload intensity, and clothing or PPE all affect how the body manages heat. A warehouse worker in PPE at a moderate temperature can be at greater risk than an office worker at a higher temperature with good ventilation and a fan. Pregnant workers, people on certain medications, those with pre-existing health conditions, and anyone doing heavy physical work are at higher risk and should be considered separately in any assessment. HSE sets out the detail in its guidance on thermal comfort and heat stress at work.
When temperatures rise, a thermal comfort risk assessment does not need to be a lengthy document. It is a practical look at how heat affects the people doing the work and what is available to manage it. Useful controls include:
For roles that work in inherently hot environments, such as kitchens, foundries, bakeries and laundries, heat should be built into the standing risk assessment rather than treated as a seasonal add-on each summer.
There is a practical case here as well as a legal one. Sustained heat is widely reported to reduce concentration and slow reaction times, which in a warehouse or manufacturing setting can translate directly into a higher accident risk, on top of the discomfort itself. Keeping people within a reasonable temperature range supports both welfare and day-to-day performance.
There is no single number that tells you when a workplace is too hot. But the absence of a legal maximum does not remove the duty to act. If heat is affecting your employees' health, safety or welfare, you are required to assess that risk and take reasonable steps to manage it, and York Green's health and safety consultancy service can help you carry out that assessment properly.