A.O. SMITH Master-Fit 100 Gallon Gas Commercial Water Heater BTR-400A A.O. Smith Master-Fit commercial gas water heaters have always provided maximum installation flexibility for both new construction and replacement applications. A.O. Smith ... The One Source Difference. BTR-400A Design Details ASME Construction The Eliminator Self Cleaning System Gallon Capacity -100 BTU/Hr. Input Natural Gas - 400,000 Height -72-1/2"" Diameter - 30-1/4"" Vent Size - 8"" Water Line Inlet Size - 2"" Side 1-1