The energetics of early weaned (13 to 16 days old) pigs were examined under four temperature regimes. The pigs, in groups of 10 (0.28 m2/pig), were housed in the indirect calorimeter chambers at initial air temperatures of 31.1, 28.9, 26.7, or 24.4°C which then were decreased by 1.1°C per week for the three weeks of the post-weaning period. The feed efficiency and average daily gain during the three-week trial for the four temperature regimes were 1.30, 360 g/day; 1.33, 380 g/day; 1.38, 370 g/day; and 1.27, 370 g/day, respectively. Overall feed efficiency was significantly lower (P < 0.05) for the coolest and warmest treatments. Average daily gain was not significantly different for any of the treatments (P > 0.05). The average moisture production for the four treatments was: 4.85, 4.26, 4.13, and 3.85 g H2O/kg-h, respectively. The total heat production and sensible heat loss were: 5.53, 2.21; 5.66, 2.71; 5.83, 3.01; and 5.87, 3.22 W/kg, respectively. Respiratory quotient averaged 0.95 to 0.96 for all regimes. All average energetic responses, except respiratory quotient, had significant differences among treatments (P < 0.05). Energetic responses of this study were substantially higher than data currently used by the ASAE Standard for swine nursery design.