Thermal discomfort distracts people from their work and causes complaints, which generate unscheduled maintenance costs. Many HVAC engineers take the cynical view that there will always be complaints, whatever they do. Recent analysis of complaints logs shows that this is not so: Federspiel (1998) demonstrated that if office temperatures had always been in the 7075°F range (21-24°C), 70 per cent of ‘hot and cold call-outs’ would not have occurred, which would have reduced maintenance costs by an estimated 20 per cent. This cost reduction represents an increase in productivity in itself, which is in addition to the undoubted productivity benefit of reducing thermal discomfort. People who feel uncomfortable lose their motivation to work and tend to take more breaks. Both of these effects reduce productivity. Many of the symptoms characteristic of sick building syndrome (SBS) become more intense and affect a larger proportion of building occupants as air temperatures rise in the 21-24°C range (Krogstad et al., 1991). People who do not feel very well do not work very well, as documented by Nunes et al. (1993), so SBS is one way by which productivity can be reduced. Cold conditions indoors cause vasoconstriction and this reduces skin temperatures. Fingertip sensitivity and the speed of finger movements are below maximum even at thermal neutrality, and other aspects of manual dexterity that can be important for productivity are progressively reduced at temperatures below neutrality – first hand-eye coordination, then muscular strength, as skin temperatures decrease in response either to lower temperatures or to prolonged exposure (Meese et al., 1982).