A passive cooling system for an electric motor drive circuit in a bathing installation, including a section of hollow pipe made of a thermally conductive tubing material, the pipe configured to form part of a water recirculation path of the bathing installation. An adapter structure has a conformal surface configured for attachment to an outer surface of the pipe and a circuit contacting surface for attachment to the motor drive circuit, the adapter structure fabricated of a thermally conductive adapter material. The adapter structure provides a thermal conductive path between the motor drive circuit and the pipe section, configured to pass heat generated by the circuitry to the pipe section and into spa water flowing through the water recirculation path, to cool the circuitry and warm the spa water.