A cooling air interface in a fan housing provided for diverting an amount of cooling air to cool a fan motor from a main air flow on a compression side of the fan, and delivering the cooling air to the fan motor to be cooled. The interface including a cooling air channel with an intake opening emptying into a cooling air passage having a cooling air exit opening where the cooling air is brought to the fan motor. Wall sections of the main air flow path that adjoin the intake opening, which in relation to the direction of the main air flow, are located upstream and downstream of the intake opening, extend up to the adjoining intake opening and into the cooling air channel, transitioning into the cooling air channel walls situated opposite one another in the form of rounded surfaces without corners and edges.