Up to 86.4% AFUE;68 to 173 Net BTUs In 6 sizes;Chimney vented;Cast iron heat exchanger, Wet base design;Tankless coil available, For domestic hot water;Metal section connectors, Resistant to chemicals, offer increased boiler longevity;Designed for ease of service, Swing-away cast iron door provides easy access to combustion chamber;10 year limited warranty