Gecko's new In.Yj-2 heat recovery (thermal transfer) system made for spas that have no heater and use the motor to heat the spa water either through friction or a heat jacket. This kit is the primary replacement for the older TDI / Tridelta / Tecmark thermal transfer systems, as well as the discontinued Len Gordon HT-1000Y2K and the Spa Builders LX-05 systems.