Solar heating units

A solar heating collector unit comprising a polygonal casing, a polygonal transparent panel closing one side of said casing, an insulation substrate disposed within the casing, a polygonal metal heat-absorbing panel having a polygonal upstanding marginal flange disposed within said casing between said insulation substrate and said transparent panel, said marginal flange extending continuously about all sides of said heat-absorbing panel and spacing said heat-absorbing panel from said transparent panel, a thermally polymerized elastomer forming a continuous polygonal peripheral joint between said transparent panel and said upstanding marginal flange and sealing said flange to said transparent panel in fluidtight relationship and securing said panels together, an inert gas sealed in the space between said panels by said elastomer, and means defining a path for heat exchange fluid against the side of said metal panel that is opposite said transparent panel.