This study aimed to evaluate the agreement of commonly reported energy metabolism measurements obtained from two different whole-room indirect calorimeters (WRICs). Nine healthy adult volunteers were evaluated over four separate 24-hour periods in a crossover design, twice in two different WRICs of different sizes, each operated according to the Room Indirect Calorimetry Operating and Reporting Standards published in 2020. The reproducibility of repeated measurements was quantified by the coefficient of variation (CV) and intraclass correlation coefficient (ICC). The CVs between and within each WRIC for average 24-hour carbon dioxide production rate (VCO2 ) and oxygen consumption rate (VO2 ), 24-hour energy expenditure (EE), and respiratory exchange ratio ranged from 1.5% to 3.6%, whereas sleep EE ranged from 3.1% to 5.5%. CVs for macronutrient oxidation rates and spontaneous physical activity were higher, ranging from 9.2% to 38.1%. ICCs of VCO2 , VO2 , 24-hour EE, and energy expenditure at zero activity were >0.95, indicating excellent reproducibility, whereas ICCs for lipid oxidation, awake and fed thermogenesis, and sleep EE ranged from 0.55 to 0.92, indicating moderate to high reproducibility. ICCs for respiratory exchange ratio and carbohydrate and protein oxidation rates were lower (<0.70). Spontaneous physical activity showed high reproducibility within chambers (ICC = 0.88) but differed substantially between chambers (ICC = 0.23). Cross-chamber reproducibility is high for common outcome measures assessed in the respiratory chamber. The results support efforts to promote standardization across WRICs to allow multicenter studies.