Abstract: A heat exchanger having a set of heat exchanging coils supported in a horizontal direction. The coils operate to exchange heat in fluids provided to the coils from a source device via a supply header tube and returned to the source device (or provided to a second device) via a return tube. A backbone supports the heat exchanging coils. Preferably, the backbone runs inside the heat exchanging coils. A bracket attached to the backbone secures a set of exchange tube supports to which the exchanging coils are attached. The heat exchanger provides a strong structure that is able to withstand currents and tidal action when mounted under a pier or in other aquatic environments. An adjustable riser device provides for flexible installation.