Employers have a legal duty to prevent injury and ill health to their employees if they are exposed to unreasonably high temperatures at work. There is no legal maximum temperature for indoor workplaces. The temperature must be "reasonable" under the Workplace (Health, Safety and Welfare) Regulations 1992.
Environmental factors (such as humidity and sources of heat in the workplace) combine with personal factors
(such as the clothing a worker is wearing and how physically demanding their work is) to influence what is called someone’s ‘thermal comfort’. Individual personal preference makes it difficult to specify a thermal environment which satisfies everyone. For workplaces where the activity is mainly sedentary, for example offices, the temperature should normally be at least 16 °C. If work involves physical effort it should be at least 13 °C (unless other laws require lower temperatures) (Regulation 7).
Workplaces need to be adequately ventilated. Fresh, clean air should be drawn from a source outside the
workplace, uncontaminated by discharges from flues, chimneys or other process outlets, and be circulated
through the workrooms.Ventilation should also remove and dilute warm, humid air and provide air movement which gives a sense of freshness without causing a draught. If the workplace contains process or heating equipment or other sources of dust, fumes or vapours, more fresh air will be needed to provide adequate ventilation. Windows or other openings may provide sufficient ventilation but, where necessary, mechanical ventilation systems should be provided and regularly maintained (Regulation 6).