The design heat load of buildings is composed of maximal heat losses via ventilation, infiltration and transmission. Ventilation control possibilities can have an impact on these maximal simultaneous ventilation losses. An automated zonally and locally controlled residential mechanical extract ventilation system (rVST) was investigated with respect to the maximal occurring total extract rate during the heating period. The analysis was performed based on big field and simulated data of a smart connected ventilation system. In that way, a reduction factor F(capacity) could be deduced that represents the maximal used fraction of the nominal installed ventilation capacity during the heating period. This reduction factor was elaborated as a function of a moving average value and percentiles, which corresponds with a negligeable chance that the maximal total extract rate is passed during the coldest winter day. Two statistical approaches when analysing the field data were compared. The reduction factor derived from simulated data corresponded very well with the field data in case of the zonal rVST. Values down to 50% were found, depending on the moving average and the percentile considered. For the local rVST, differences in reduction factor were significant between simulations and practice, due to a more complex and variable system to model. The reduction factor of the local compared to the zonal rVST is on average and relatively 14% and 28% lower, based on respectively field data (analysis 2) and simulation data. The installed ventilation capacity, however, in case of the local rVST is about 40% higher.