The hermetically closed-looped system consists primarily of a vertical cylindrical combustion chamber, coil, burner and supply and return manifolds. Chamber walls are lined with vertical pipes with continuously-welded longitudinal fins. The pipes are connected to a lower manifold (fed with condensate) and upper manifold (connected to the steam outlet). Often designed to section VIII Division 1, the heater remains flooded with fluid through the systems level control. This eliminates the need for boiler operation.