21-9074-1-0311 is a part number for a Concord SB-50 steam boiler. It is an atmospheric vent model with up to 50,000 BTU input and natural gas fuel. The SB-50 features a cast iron heat exchanger, an aluminized steel combustion chamber, and is approved for use with 2, 3, or 4-pipe systems. This part also includes multiple safety systems such as pressure and temperature limit controls, high limit and motorized aquastat, and a flame safeguard control.