By creating a pressurized environment in the combustion chamber, the air intake system in the Effex high-efficiency gas water heater extracts additional heat from exhaust gas as it passes through the unit. The result is a higher percentage of heat transferred to the water, for a 0.7 Energy Factor and less wasted energy. Available in 40- and 50-gallon capacities, the Effex installs with the same gas, water, and venting connections as a standard model, making it ideal for replacement installations. A.O. Smith | 800.527.1953 | hotwater.comhttp://www.hotwater.com