Collector panel for solar heating system

A collector panel for a solar heating system, comprising two elongated rectangular metal sheets bonded together in face-to-face relation except along elongated narrow areas defining between the sheets a network of conduits for a moving heat absorbing liquid, the network comprising two parallel conduits extending along the opposite longitudinal edges of the panel and providing inlet and outlet headers for the liquid, a plurality of parallel conduits extending longitudinally of the panel intermediate and parallel to the header conduits, and a plurality of conduits extending transversely of the panel and interconnecting the headers and the intermediate longitudinal conduits, the transverse conduits being arranged in tiers extending longitudinally of the panel between the headers and the intermediate conduits, each of the transverse conduits being disposed angularly to the headers and intermediate conduits throughout at least part of its length.