Model order reduction (MOR) techniques play a crucial role in the computer-aided design of modern integrated circuits, where they are used to reduce the size of parasitic networks. Unfortunately, the efficient reduction of passive networks with many ports is still an open problem. Existing techniques do not scale well with the number of ports, and lead to dense reduced models that burden subsequent simulations. In this paper, we propose TurboMOR-RC, a novel MOR technique for the efficient reduction of passive RC networks. TurboMOR-RC is based on moment-matching at dc, achieved through efficient congruence transformations based on Householder reflections. A novel feature of TurboMOR-RC is the block-diagonal structure of the reduced models, that makes them more efficient than the dense models produced by existing techniques. Moreover, the model structure allows for an insightful interpretation of the reduction process in terms of system theory. Numerical results show that TurboMOR-RC scales more favorably than existing techniques in terms of reduction time, simulation time, and memory consumption.