Copper-Fin II commercial gas water heaters, models 401-751, have proportional firing systems, multiple venting options and low NOx ratings. They have 85% thermal efficiency ratings and can provide peak performance even at low operating outputs. The proportional firing system provides a measured response to demand, while always maintaining the ideal gas/air ratio. A controller allows the heater's system to digitally monitor hot water demand and automatically adjust blower output and gas valves. The units will fit through standard 36-in. doorways intact.