To have "thermal comfort" means that a person wearing a normal amount of clothing feels neither too cold nor too warm. Thermal comfort is important both for one's well-being and for productivity. It can be achieved only when the air temperature, humidity and air movement are within the specified range often referred to as the "comfort zone".
Where air movement is virtually absent and when relative humidity can be kept at about 50%, the ambient temperature becomes the most critical factor for maintaining thermal comfort indoors. However, temperature preferences vary greatly among individuals and there is no one temperature that can satisfy everyone. Nevertheless, an office which is too warm makes its occupants feel tired; on the other hand, one that is too cold causes the occupants' attention to drift, making them restless and easily distracted.
Maintaining constant thermal conditions in the offices is important. Even minor deviation from comfort may be stressful and affect performance and safety. Workers already under stress are less tolerant of uncomfortable conditions.
A general recommendation is that the temperature be held constant in the range of 21-23°C (69-73°F). In summertime when outdoor temperatures are higher it is advisable to keep air-conditioned offices slightly warmer to minimize the temperature discrepancy between indoors and outdoors.
Relative humidity levels below 20% can cause discomfort through drying of the mucous membranes and skin. Low relative humidity levels may also cause static electricity build-up and negatively effect the operations of some office equipment such as printers and computers. Relative humidity levels above 70% may lead to the development of condensation on surfaces and within the interior of equipment and building structures. Left alone, these areas may develop mould and fungi.
Air velocities below 0.25 metres/second (or about 50 feet/minute) does not create any significant distraction even in tasks requiring sustained attention.
The CSA Standard CAN/CSA Z412-00 (R2011) - "Office Ergonomics" gives acceptable ranges of temperature and relative humidity for offices in Canada. These values are the same as recommended by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 55 - 2010 "Thermal Environmental Conditions for Human Occupancy". The recommended temperature ranges have been found to meet the needs of at least 80% of individuals. Some people may feel uncomfortable even if these values are met. Additional measures may be required.
|Temperature / Humidity Ranges for Comfort|
|Conditions||Relative Humidity||Acceptable Operating Temperatures|
|Summer (light clothing)||If 30%, then |
If 60%, then
|24.5 - 28 |
23 - 25.5
| 76 - 82 |
74 - 78
|Winter (warm clothing)||If 30%, then |
If 60%, then
|20.5 - 25.5 |
20 - 24
|69 - 78 |
68 - 75
Source: Adapted from ASHRAE 55-2010.
Document last updated on April 5, 2013