The Hayward H-Series W3H400FDN Natural Gas Pool and Spa Heater is environmentally friendly and energy efficient. Boasting an industry leading 84 percent thermal efficiency the environmentally friendly H-Series complies with all current California and Texas air quality emission standards. It is also the only pool heater to offer Cupro Nickel heat exchangers standard on all models. Cupro-Nickel is designed to withstand the harshest pool environments like low pH, high flow and heavy pool use and is also recommended for all pools using salt systems. Features: For In-Ground Pools and Spas Electronic Ignition Dual Thermostat 400K BTU Natural Gas (NG) Cupro Nickel Heat Exchangers Easy-to-read L.E.D. digital Control Panel New polymer header provides superior hydraulic performance Larger diameter plumbing systems with 2" x 2.5" CPVC unions Meets the NOx Emission standards