There is an opinion about the inevitability of unstable operation of local ventilation fans in the presence of a hump in their characteristic. When determining the mode of operation of the fan in the network does not take into account the leakiness of the pipeline, which introduces some features in the calculation methodology, which is not sufficiently developed and not brought to a form convenient for practice.To clarify these issues and made an attempt to develop a methodology for determining the mode of operation of the local ventilation fan and its stability.