Intensive pig housing often provides an environment with high levels of airborne contaminants which may be to the detriment of the health and welfare of the pig and the stockman. The problem is compounded by producers maintaining higher temperatures than necessary in an attempt to maximise performance. Consequently, air changes in a room may be unduly limited, particularly when the temperature differential between the outside and inside is large as in winter. It is therefore desirable to keep the room temperature as low as possible to maximise ventilation rate whilst ensuring that feed is used efficiently for growth. The temperature above which this occurs is the lower critical temperature (LCT). However current recommendations for LCT are based on research carried out on individuals and very small groups. Commercially, the variability of the group may have a significant effect on the practical minimum temperature which may be achieved. The objective of the trial reported here was to assess the performance of larger groups of pigs grown in controlled conditions utilising current recommendations for LCT based on the Bruce and Clark (1979) model.