Human physiology is developed before our ancestors started creating indoor environments. Our bodies are designed to function well in environments where there is temperature variation. Human thermo-regulatory processes are stimulated when the temperature indoors varies within the comfort range (see section 3.1.4). In most buildings, the temperature increases during the day as the outdoor temperature increases. Sunlight through windows increases the temperature, while overcast weather can reduce the temperature. The seasons also have an impact, as the temperature is often cooler in winter than in summer.

Recent research shows that slightly cool temperatures (e.g. at or below 20°C) may stimulate unnoticeable shivering, which increases metabolism. As obesity is becoming an increasing problem, increased metabolism can have a positive health impact (van Marken Lichtenbelt et al., 2009; Bluyssen, 2013).

A “sunroom” can be the space in a home where temperatures vary the most and where it is most enjoyable and healthy to spend time.

The temperature in the bedroom has an impact on sleep quality. There are large personal and cultural variations in preference. Some prefer always to have their bedroom window open and the heating switched off, even in mid-winter, while others prefer the bedroom temperature to be the same as in other rooms of the house. Some prefer thin sheets or blankets, while others prefer a thick duvet.

Surprisingly few studies give a scientific response to this discussion. There is no clear guideline as to what temperature and bedding will give the best sleep quality. What is known is that overheating reduces sleep quality. The bedroom should not be too warm, and it is particularly important that the time at which you fall asleep is not too warm. CIBSE Guide A states that sleep may be impaired above an operative temperature of 24°C (Laverge et al., 2011; CIBSE, 2006).