A method of estimating a ventilation rate in a room, the method comprising receiving a signal indicative of a concentration of at least one Volatile organic compound (VOC(t)) inside the room； processing the signal to detect at least one increase from an initial level (VOC(t0)) of the concentration of the at least one volatile organic compound； detect a corresponding maximum level of the concentration from the initial level； detecting when the concentration of the volatile organic compound returns to the initial level or a steady state level (VOCss) from the corresponding maximum level； and determining the ventilation rate (k) based on the time (t) taken by the concentration of the at least one Volatile organic compound to reach to the initial level from the corresponding maximum level.
