Rheem Professional Classic Atmospheric Series 40 Gallon Capacity 40,000 BTU Heating Input Tall Gas Water Heater This water heater does not meet the ultra low NOx (ULN) emissions requirements for some California residents. Regulations prohibit the sale, shipment, or installation of this water heater in any air quality district that requires ULN water heaters Exclusive air/fuel shut-off device Natural gas water heater costs less to operate than electric models Exclusive air/fuel shut-off device|Natural gas water heater costs less to operate than electric models