The air temperature of the laboratory and working rooms should ideally be maintained at a constant level (preferably between 18 and 25°C) and the humidity should also be kept reasonably steady at about 50%.

The air temperature of the laboratory and working rooms should ideally be maintained at a constant level (preferably between 18 and 25°C) and the humidity should also be kept reasonably steady at about 50%. In many tropical countries air conditioning of the whole building is virtually as essential as central heating in cold and temperate countries, while in countries having a continental climate with hot summers and cold winters, both air cooling and central heating are necessary.
The importance of supplying clean air, at a constant favourable temperature and humidity to all parts of a scientific laboratory building is too often neglected for financial reasons, particularly in tropical countries where air conditioning on a large scale during the hot seasons may be very expensive. However, if some form of air conditioning is not provided, the efficiency of the work done is bound to be reduced and other expenses incurred through a number of factors:

1. Analytical processes normally carried out at room temperature can be affected by differences in temperature so that an analysis performed in a "cold" room can give a different result to one performed in a "hot" room. The temperature of distilled or deionized water may be very different from that in the laboratory. The extraction of phosphate, for example, may be influenced by temperature. Control of temperature is possible on a small scale by the use of thermostatic waterbaths or immersion coolers but this is impracticable for shaking machines or other large scale routine operations. Temperature correction factors can, of course, be applied in some cases but these have to be established first and may be inaccurate for wide temperature variations. 2. Many chemicals are affected by the temperature and humidity conditions under which they are stored, particularly if these conditions fluctuate. Thus, a substance may absorb water from humid air or effloresce in dry air or decompose at high temperatures, becoming either useless or needing purification.
3. Modem scientific instruments can be quickly and permanently damaged by changes in temperature and humidity, which often cause condensation, tarnishing and short-circuits.
4. The efficiency of all laboratory personnel is undoubtedly reduced by abnormally high or low temperatures or high humidity and by the presence of even moderate amounts of dust or chemical fumes in the air, thus affecting output both in quantity and quality.

5. Central air conditioning is preferred to the use of obviously cheaper alternatives such as individual cooling units or heaters in each room. Almost inevitably, corridors, store rooms and, often, sample preparation rooms are ignored and this may lead to undesirably wide differences in temperature and humidity between such places and analytical laboratories. For instance the moisture condition of a sample kept in a hot and humid store room (or a very cold one) may change significantly when taken to an air-conditioned laboratory. The effects of storage on the results of analysis of soil samples, as often noted in the literature, may vary with temperature and humidity.