Vesta. DS’ premium condensing tankless water heaters are CSA, AHRI and NSF certified, feature a 0.95 UEF, low NOx and are lead free. Vesta Smart Technology VRP models include a built-in Grundfos pump and a 1/2-gal. buffer tank for internal or external loop recirculation (Title 24 compliant with an optional controller). VST models are designed for North America for use in single residential or in multiple commercial applications. Cascade up to 40 units (7,500k Btu/h).