Get Years Of Dependable, Low-Cost Hot Water! Ultra-Low NOx Gas Water Heaters Introducing Natural Gas Ultra-Low NOx Reliance® Water Heaters, which use the latest technology, an enhanced combustion system, and high temperature materials to meet the new South Coast Air Quality Management District NOx emission requirements. Reliance® Ultra-Low NOx Water Heaters leverage Flammable Vapor Ignition Resistant technology, offer a flexible three/four inch venting option, and operate smoothly, efficiently, and quietly. Ultra-Low NOx Reliance® Water Heaters are offered in 30-, 40-, and 50-gallon models. Back to gas water heaters