Abstract: A radiant burner includes a housing for receiving a combustible air and fuel mixture and a combustor unit formed to include an open-space combustion chamber having a top opening and passageways for communicating the combustible air and fuel mixture from the housing to the open-space combustion chamber. The combustor unit is a block of insulation material formed to include a cavity defining the open-space combustion chamber and a plurality of apertures defining the passageways. The combustible air and fuel mixture extant in the open-space combustion chamber is ignited to produce a flame. The top opening of the open-space combustion chamber is covered to define a flame retention region therein so that the flame is stabilized in and contained wholly within the open-space combustion chamber.