Heat and moisture production (HMP) values are used to size ventilation fans in animal housing. The HMP values that are currently published in the ASABE standards were from data collected in the early 1950s. This study is one of a series of studies being conducted to update the HMP values for the ASABE and ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) Standards. This study focused on the HMP measurements on growing gilts in the weight range of 60 to 120 kg over a temperature range of 16 to 32°C. Thirty gilts selected on the basis of weight and health status were placed in one of five environmental chambers and in one of six pens in each chamber. Heat production rate (HP) was determined using indirect calorimetry methods after the animals were acclimated for 2 weeks to a particular temperature. Each measurement was made on an individual animal over a 21-hr period. It was determined that HP decreased, feed intake decreased, and moisture production (MP) increased as environmental temperature increased. HP was directly affected by the level of feed consumption. Dynamic measurements showed a diurnal HP pattern in that it was higher during light period than during dark period, with an immediate increase as the lights were turned on. Results on nursery age animals will be reported in a companion study.