Dunkirk H2Oi40LDK 40 Gallon Indirect Water Heater With Lowboy. 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 Single Coil Indirect Water Heater is available from 30 to 115 gallon capacity, with 316L stainless steel construction and top connections for an easy installation. This water heater is so well insulated that the water will lose only a half-degree for every hour it stands by. The smooth coil design prevents sediment build-up.