This compression adapter is necessary for integrating a heater into the Current USA 1/4HP Prime Inline Aquarium Chiller (Dual Stage Controller) and Current USA 1/3HP Prime Inline Aquarium Chiller (Dual Stage Controller). Each of the Chillers can take one or two heaters. We recommend using the Hydor Theo 200 watt Heater (other heaters may work, but the Theo is the only heater we carry that will work).Product Manual (pdf file in new window)