Specifications include, but are not limited to: The heat exchanger shall be of a single-bank, vertical multi-pass design and shall completely enclose the combustion chamber for maximum efficiency. The tubes shall be set vertically and shall be rolled into a powder-coated, ASME water heater quality, carbon-steel tube sheet. The heat exchanger shall be sealed to 160 PSIG rated bronze headers with high-temperature silicone "O" rings. The low water volume heat exchanger shall be explosion-proof on the water side and shall carry a twenty-year warranty against thermal shock. The headers shall be secured to the tube sheet by stud bolts with flange nuts to permit inspection and maintenance without removal of external piping connections. A heavy gauge stainless steel slotted heat exchanger wrap shall ensure proper combustion gas flow across the copper-finned tubes.