Hayward H-Series H2101 Millivolt Pool Heater; Natural Gas, 210K BTU. Features on all millivolt heaters include rust-resistant water path with polymer header assembly and a rapid-heat combustion chamber. They are easy to install and maintain, thanks to its low profile, lightweight and CPVC plumbing capabilities. H-Series heaters are all equipped with a Cupro Nickel Heat Exchanger for efficient heating and superior durability. Cupro Nickel provides improved durability and longevity against the damaging effects of erosion that can occur under high-flow conditions, corrosion from occasional pool chemical imbalances, and is ideal for salt-chlorinated pools. For extra protection, the cupro nickel material has been coupled with an improved flow rate by-pass control. Together, these added technological improvements ensure that your Hayward heater outperforms and outlasts expectations.