This work gives the definition of the coefficient of resistance of the ventilating ducts as well as of the influence on the value of this coefficient of the curve of the interior and exterior angles of bending, of the grade of widening and of the sloping of the interior angle. It contains also the curves for calculating the coefficient of resistance of all kind of bending. The meaning of coefficients of resistance with the simultaneous expansion of air should be taken on the base of curves represented on fig. 2 and 3. Interior and exterior angles of turns should have rounded edges. The coefficients of resistance in this case also can be seen on the curves shown on fig. 2 and 3. It is recommended to the interior angles of turns. The size of the cut and the coefficients of resistance for this case should be taken on the curve, given on fig. 6. If the shaft is used for the purpose of ventilation only and is not used for hoisting then it is rational to lock the part of the shaft located above the air channel of ventilator.