A method of determining an optimal filter life cycle between replacements of a filter in a ventilation system, comprising performing the following steps in a processing device: receiving at least one filter hardware value (C filter), representing an amount of a resource associated with at least production of the filter, receiving at least one filter use value (C use), representing an amount or rate of said resource associated with use of the filter, receiving a plurality of measured data points (M[i]), each representing a measured pressure drop (M[i] p) over the filter at a respective time (M[i] t), and determining the optimal filter life cycle by minimizing a total filter resource consumption composed of: a first factor (Filter annual_cost [i]), according to which the resource consumption is inversely proportional to the filter life cycle, a second factor (Energy annual_cost [i]), according to which the resource consumption is directly proportional to the filter life cycle, providing a plurality of predicted data points, each representing an predicted pressure drop over the filter at a respective future point in time, characterised by grouping successive measured data points (M[i]) into windows, each window comprising at least one of the measured data points (M[i]), for each window identifying a maximum pressure drop, and assigning the identified maximum pressure drop as a maximum pressure drop (max_values[i]) for all measured data points (M[i]) of that window; for each measured data point (M[i]) estimating an air flow (Q[i]) based on the maximum pressure drop (max _values[i]) and the measured pressure drop (M[i] p) of the respective measured data point (M[i]), and deriving the second factor (Energy annual_cost [i]) based on the filter use value (C use), the measured data points (M[i]), the predicted data points and the estimated air flows (Q[i]). receiving at least one filter hardware value (C filter), representing an amount of a resource associated with at least production of the filter, receiving at least one filter use value (C use), representing an amount or rate of said resource associated with use of the filter, receiving a plurality of measured data points (M[i]), each representing a measured pressure drop (M[i] p) over the filter at a respective time (M[i] t), and determining the optimal filter life cycle by minimizing a total filter resource consumption composed of: a first factor (Filter annual_cost [i]), according to which the resource consumption is inversely proportional to the filter life cycle, a second factor (Energy annual_cost [i]), according to which the resource consumption is directly proportional to the filter life cycle, providing a plurality of predicted data points, each representing an predicted pressure drop over the filter at a respective future point in time, characterised by grouping successive measured data points (M[i]) into windows, each window comprising at least one of the measured data points (M[i]), for each window identifying a maximum pressure drop, and assigning the identified maximum pressure drop as a maximum pressure drop (max_values[i]) for all measured data points (M[i]) of that window; for each measured data point (M[i]) estimating an air flow (Q[i]) based on the maximum pressure drop (max _values[i]) and the measured pressure drop (M[i] p) of the respective measured data point (M[i]), and deriving the second factor (Energy annual_cost [i]) based on the filter use value (C use), the measured data points (M[i]), the predicted data points and the estimated air flows (Q[i]). a first factor (Filter annual_cost [i]), according to which the resource consumption is inversely proportional to the filter life cycle, a second factor (Energy annual_cost [i]), according to which the resource consumption is directly proportional to the filter life cycle, providing a plurality of predicted data points, each representing an predicted pressure drop over the filter at a respective future point in time, characterised by grouping successive measured data points (M[i]) into windows, each window comprising at least one of the measured data points (M[i]), for each window identifying a maximum pressure drop, and assigning the identified maximum pressure drop as a maximum pressure drop (max_values[i]) for all measured data points (M[i]) of that window; for each measured data point (M[i]) estimating an air flow (Q[i]) based on the maximum pressure drop (max _values[i]) and the measured pressure drop (M[i] p) of the respective measured data point (M[i]), and deriving the second factor (Energy annual_cost [i]) based on the filter use value (C use), the measured data points (M[i]), the predicted data points and the estimated air flows (Q[i]).