A. O. Smith’s Simplicity Series of concentric venting, noncondensing tankless water heaters is designed to make installations simple and flexible through a gas-convertible combustion system — from natural gas to propane with all necessary components already in the box. Available in 140K, 190K and 199K Btu versions and ULN-certified, the series scores a 0.82 Energy Factor rating. These models also come equipped with integrated controls that make temperature adjustment and diagnostic review easier.