This paper studies the sensitivity of heat losses in collective heat distribution systems using a simplified calculation method. The approach is applied to a specific type of heat distribution system where the network distributes heat for both space heating and sanitary hot water. The proposed methodology takes design parameters influencing the thermal performance of the heat distribution system into account. Among other parameters, the recirculation control strategy and the length of service pipes are taken into account. The present study assesses the impact of potential variations in the input parameters on the total heat loss and distribution efficiency. To that aim, a simulation study was conducted with a multilevel factorial design, consisting of the combinations of parameters which were varied from the levels at which they were set. Results show how sensitive the solution is to the different parameter values. Furthermore, the potential of the improved calculation method, which allows combining different design conditions within a single heating distribution system, was demonstrated.