The increasing penetration of distributed generation into the power distribution domain necessitates reliable and QoS-aware communication in order to safely manage the grid. To achieve this, heterogeneous networks (a combination of the Internet and private networks) offer a promising approach due to the potential cost effectiveness and leveraging the ubiquitous coverage. However, the current Internet infrastructure does not support end-to-end (E2E) QoS-guaranteed communication. To cope with this challenge, we propose a novel overlay network architecture, termed HetGrid, with a dedicated QoS routing mechanism. It provides QoS guarantees across the network, taking into account three parameters: reliability, latency and bandwidth for power distribution grid applications. To achieve this, we also develop two elements, namely (a) multipath routing mechanism compensating the critical applications for their high reliability requirements by employing E2E physically-disjoint paths, and (b) altruistic resource allocation with the QoS routing mechanism targeting QoS-guaranteed communication for applications having strict QoS requirements. Our results demonstrate that the proposed overlay network approach provides highly efficient, reliable and QoS-aware communication in heterogeneous networks. © 2015, Springer Science+Business Media New York.