A thermosyphonic heat recovery unit for thermosyphonic heat transfer of heat from a hotter first fluid to a cooler second fluid comprising a heat exchanger including a first fluid conduit and a second fluid conduit, optimized means for connecting fluids to the two conduits to optimize heat transfer and fluid flow, a pressurized cold fluid input and hot fluid output, whereby the second fluid thermosyphonically flows through said second conduit as the first fluid flows through said first conduit. Said system having an optimized heat exchanger tube-on tube spirally wound, with wind direction to take advantage of the Coriolus force effect, for optimized refrigerant and other fluid turbulence and therefore optimized heat transfer, and optimum location of said heat exchanger and sizes of connecting tubes to minimize refrigerant friction related pressure loss, and to optimize heat transfer, refrigerant flow and thermosyphonic second fluid flow through said heat exchanger.