Copyright Goodheart-Willcox Co., Inc. 252 Hydronic Heating: Systems and Applications where the tubing is looped around each row, Figure 12-28. When all panels are secured, vacuum the grooves where the tubing is to be inserted and apply a bead of silicone into each groove. Lay the tubing into the grooves before the silicone dries. Protect the tubing where it penetrates any floor open- ings by installing plastic sleeves through the floor penetra- tions. Connect the individual zoned circuits to the manifold station and pressure test each circuit for leaks. Once all pan- els are installed and circuits tested, the room is ready for its finished floor covering, Figure 12-29. 12.4.4 Below-Floor Suspended Tubing Systems An alternative to prefabricated radiant floor panels is to install the radiant system below the existing flooring using below-floor suspended tubing. This installation is similar to the procedure for installing above-floor radiant panels and can be accomplished with new construction projects or as a retrofit. In this type of installation, heat is transferred from the bottom of the flooring and through the tubing to the floor above, Figure 12-30. 12.4.4.1 Installing Below-Floor Suspended Tubing Systems One installation method for the below-floor radiant heating system is to install the PEX or PE-RT tubing within the underfloor joist cavity using pipe hangers fastened either to the sides of the floor joists or to the underside of the subfloor- ing. The floor joists are drilled on opposite ends of the room and tubing is pulled through the joist space, looping the tubing from one joist bay to the next as necessary. After installing the tubing through the last joist cavity, it is run back to the floor opening and connected to the manifold station. The tubing can also be attached to the floor joists or to the underside of the subflooring using PEX clips spaced 8″ on center for 16″ joist bays and spaced 3′ apart. Avoid placing the tubing directly onto the underside of the subflooring as this can produce hot Dmitry Melnikov/Shutterstock.com Figure 12-27. Once the prefabricated floor panel system is designed, set the panels in place and secure them firmly. Viega, LLC Figure 12-28. Be sure that end panels are staggered to avoid creating any dead-end circuits where the tubing is looped around each row. vchal/Shutterstock.com Figure 12-29. Once all panels are installed and circuits tested, the room is ready for its finished floor covering.