An integrated method for assessing metabolic rate and maintaining indoor air quality and efficient ventilation energy use. A physical sensor assesses room occupancy. An actuated ventilation system is set to a constant CO2 level in a predetermined healthy range, where the actuated ventilation system includes a CO2 sensor. The actuated ventilation system sets a first air ventilation rate and the sensor measures a first CO2 level. The system determines whether CO2 level is in a healthy range, if not then the CO2 level is adjusted by setting a subsequent air ventilation rate. A subsequent CO2 level is measured. If the CO2 level is determined to meet a predetermined healthy range, then an assessment of change of air ventilation rate (Δ ACH) is determined. The determination of air change rate can be further augmented by a physical pressure based measurement. The overall metabolic rate is generated.