A submersible heat-exchanging apparatus for installation into storage tanks used for containing industrial oils. The apparatus comprises a cylindrical heat-exchange component with one end sealingly engaging a terminal plug and the other end sealingly engaging and communicating with a coupling manifold having opposed inflow and outflow ports. A flow-directing elongate insert is provided with one end configured to engage the coupling manifold interposed the inflow and outflow ports, and the other end provided with an aperture and configured for abutting the terminal plug. The flow-directing elongate insert slidingly contacts and cooperates with the inner walls of the heat-conductive conduit thereby partitioning the heat-conductive conduit into two opposed fluid transmission channels wherein one channel communicates with the inlet port and the other channel communicates with the outlet port. The coupling manifold sealingly engages an aperture provided in the storage tank whereby the heat-exchange component extends into the tank.