KNXnet/IP allows integration of different KNX networks through IP; this is achieved by the use of a particular device called KNXnet/IP Router. Due to the different transmission speeds among KNX network and the IP medium, a flow control mechanism to prevent the congestion of KNXnet/IP Router has been recently foreseen by the standard. In this paper, the authors present some preliminary results about a performance evaluation of the KNXnet/IP flow control mechanism, based on the use of a particular kind of stochastic Petri Nets, called Stochastic Activity Networks (SAN).