Dunkirk H2OBT402DK 40 Gallon Buffer Tank With 2" Connection. Since the late 1920's, Dunkirk has delivered innovative, efficient and dependable home heating systems to professionals, building owners and homeowners. This is the best way to deliver heating equipment that lasts and reduces home heating costs. Dunkirk's H2O Stainless Steel Hydronic Buffer Tanks are available in 40-, 60-, 80-, or 115-gallon capacity, with your choice of 1-1/4", 1-1/2", or 2" connections for peak performance. These Buffer Tanks are Ideal for Low Mass Boilers.