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, the leakiness of the pipeline is not taken into account, which introduces some features into the calculation methodology, which is not sufficiently developed and has not been brought to a form convenient for practice. To clarify these issues, an attempt has been made to develop a methodology for determining the mode of operation of the local ventilation fan and its stability.