Delivering 96% efficiency, the 100,000 BTU John Wood Envirosense Power Direct Vent gas water heater is equipped with a fully submerged, spiral-shaped condensing heat exchanger and 50 gallons of storage capacity. This design provides much greater heat transfer surface than a standard straight flue tube, resulting in 96% thermal efficiency and higher hot water output* than comparable 80% efficient water heaters. With a 22? diameter, the Envirosense Power Direct Vent can be installed in less space than a 75-gallon unit yet delivers greater recovery and lower operating costs.