1. A metal burner assembly comprising a base plate element, a burner head including inner and outer shell elements, and an end cap element, said elements being formed of uniform, thin-walled metal stock, at least one of said elements having a circular peripheral edge, another of said elements having an annular surface portion, said peripheral edge being in gastight metal-tometal contact with said annular surface, a portion of said base plate element cooperating with said inner and outer shell elements to define a plenum chamber therewith, said base plate element including a first aperture associated with said outer shell element and a second aperture associated with said inner shell element, said base plate element having a porcelain coating, the peripheral edges of said first and second apertures being in metal-to-metal gastight sealing engagement with said outer shell element and said inner shell element respectively, the sheet metal wall of said base plate element forming said peripheral edges obliquely engaging the associated surface portions of said outer and inner shell elements.

3. A burner assembly comprising a base plate and a burner head, said base plate and burner head being formed of sheet or uniform, thin-walled metal stock, said base plate having a porcelain enamel coating, said base plate having an aperture defined by a circular peripheral edge, said edge being in direct gastight sealing engagement with a wall portion of said burner head, a wall of said base plate forming said peripheral edge being oblique to said burner head wall portion, whereby a circumferential corner of said peripheral edge substantially free of porcelain enamel coating engages said burner head wall portion.

4. A sheet metal burner assembly comprising a base plate and a plurality of burner heads mounted on the base plate, the base plate being formed of a pair of overlying steel sheets secured together, at least one of said sheets being embossed with integral air-gas ducts for each of said burner heads extending from an inlet and to a burner head location, at least one of said sheets being embossed with integral ignition tubes extending from a pilot housing to each of said burner heads, said base plate sheets having a porcelain enamel coating applied after being secured together, said coating covering the exterior surfaces of the base plate and the interior of said ducts and said tubes, said coating forming a gastight seal at an interface between said sheets in said ducts, an annular embossment in one of said sheets at each burner head location forming a plenum chamber with the interior of the associated burner head and communicating with an associated duct, a pair of aligned apertures in said sheets at each burner head location, one of said apertures being centrally formed in said annular embossment and the other aperture being formed in the other sheet, each burner head having an inner and an outer shell of uniform, thin-walled steel stock, said inner and outer shells being respectively joined with a first and second of said apertures to define with said embossment said plenum chamber, an annular cap element extending between the inner and outer shells at their upper ends to form an upper end wall of the plenum chamber, said outer shell including burner flame apertures adapted to release an air-gas mixture from said plenum, at least portions of the walls of said inner and outer shells being free of porcelain enamel coating and being obliquely engaged by the wall portions of said sheets defining said apertures whereby the peripheral edge corners of the apertures of said sheets, being substantially free of porcelain enamel coating, provide a gastight metal-to-metal seal at said apertures.