The QHMVPOR plugs into the QHMZ4A, QHMZ6A, QHMZ4P and QHMZ6P panels, (Panels Sold Separately), to control the fluid temperature that goes to the Radiant Panel. It does this by adjusting the speed of a pump, (Pump Sold Separately), that is injecting hotter fluid into the Radiant loop which requires a cooler fluid temperature. The QHMVPOR comes with a supply sensor that monitors the fluid ...