Link your heating system to the ½” FNPT connection. Connect directly a heating expansion tank (HGT-15, HGT-30, HGT-60M or HGT-60), with the Service valve (HGSV12) on the ½” FNPT connection. Then, on connections (1⁄8” FNPT), connect an automatic air vent (R8818) and a pressure gage (GAGE0-30BOTTOM or GAGE0-100BOTTOM). On connection (½” MNPT) you can either connect your GMP or simply the cold water supply.