An indirect calorimetry trial examined the energetic efficiency of cattle supplemented zilpaterol hydrochloride (ZH). Beef steers (n = 20; 463 ± 14 kg) blocked (n = 5) by weight and source were individually fed and adapted to maintenance intake (MI; {[(BW×0.891)^0.75 × 0.077]/diet NE_m, BW d −1 and 1}) for 21 d before ZH (90 mg/hd/d) or non-ZH treatment for 20 d (455 ± 14 kg, SOT). During the 21d maintenance period, MI was adjusted based on BW (d −1, 1 vs. d 4, 5, 9, 10, 14, 15, 19 and 20) after 10h water and feed withdrawal (no feed remained for any animals at start of withdrawal periods). Intakes were not adjusted during 20 d treatment period. Respiration chambers were used to quantify energetics for maintenance (d12–16 of ZH period) and fasting heat production (FHP; d19–20 of ZH period, total 4d fast). Daily feed and fecal samples were analyzed for gross energy (GE); urine was analyzed for nitrogen and GE was calculated from the energetic value of urea. Data were analyzed as a mixed model with fixed effect of ZH treatment and random effects of block and chamber. No difference in DMI, O₂ consumption or CH₄ production (P > 0.10) was detected between treatments but ZH cattle had higher CO₂ production (P = 0.04; 2325 vs. 2185 L/steer; 23.6 vs. 22.4 L/kg BW^0.75). During FHP, O₂ consumption was not affected (P > 0.10) by treatment whereas CO₂ production (L/steer) increased with ZH treatment (P = 0.04; 1423 vs. 1338 L/steer). Gross energy, fecal energy, digestible energy and methane energy did not differ between treatments (P > 0.10), however urinary energy was higher (P = 0.05; 0.091 vs. 0.074 Mcal) in control cattle. There was no difference in metabolizable energy between treatments (P > 0.10). Heat production tended (P = 0.09) to increase for ZH treated cattle (12.44 vs. 11.69 Mcal, respectively) on an absolute basis, but not on a BW^0.75 basis (P = 0.12; 0.126 vs. 0.120, respectively). No difference in FHP was detected between treatments (P = 0.32). Results from this trial indicate that ZH treatment tends (P = 0.09) to modify heat production during maintenance by increasing CO₂ production (P = 0.04).