Abstract: A heating system for producing heat by the gasification of solid, organic biomass materials. A mass of such materials is maintained on a grate in a primary oxidation chamber of the catalytic type, and materials in such mass are gradually heated in a deficiency of oxidation for full oxidation of such materials to produce a gaseous, combustible effluent. The gaseous combustible effluent is transferred through an insulated exit duct to a secondary oxidation chamber where it is further oxidized to a fully oxidized state by burning. In one embodiment, the insulated exit duct has a restricted inlet portion within the primary oxidation chamber to serve as a flame deflector. The gaseous effluent from the secondary oxidation chamber is used as a heat source for a water tube boiler. A storage hopper is provided to store the biomass feed materials for delivery to the primary oxidation chamber. The bottom of the storage hopper is inverted and reciprocating plates are provided along the bottom of the storage hopper.