Copyright Goodheart-Willcox Co., Inc. Chapter 12 Radiant Heating Systems 251 zone as outlined for slab-on-grade systems. When all tubing circuits are deter- mined to be leak-free, spray the floor with a layer of sealant and bond coating to minimize water absorption into the subfloor. This will also strengthen the bond between the subfloor and concrete. The concrete or gypsum underlayment material is now prepared and mixed outside of the building, then poured over the tubing circuits. The poured mixture is typically quite fluid, and when installed it becomes self-leveling with mini- mum floating necessary, Figure 12-25. Once cured, the finished floor product resembles plaster and is very hard and durable. It can be covered with almost any flooring finish including carpeting, vinyl sheeting, ceramic tile, or glued-down wood flooring. Always follow the finished flooring manufacturer’s instructions for proper installation over a thin-slab floor. 12.4.3 Above-Floor Prefabricated Panels Prefabricated radiant floor panels provide another alternative to slab-on- grade radiant floor installations. Several manufacturers fabricate these types of panels, which are designed to fit over an existing wooden subfloor or over slab- on-grade concrete—such as in a basement, Figure 12-26. Prefabricated panels can be used where the existing floor cannot support the additional weight of a thin-slab installation or where the finished flooring requires a large number of fasteners for completion. Prefabricated radiant floor panels are essentially heat transfer plates. They consist of wooden or plywood panels with notched grooves that are designed to hold 5/16″ to 1/2″ PEX or PE-RT tubing in place. Sheets of aluminum on the underside of these panels enhance the heat transfer between the tubing and the flooring. 12.4.3.1 Installing Above-Floor Prefabricated Panel Systems The installation of a prefabricated floor panel system begins with designing and laying out the zones to be heated. This will reduce installation time and the amount of materials used. Once the floor surface is thoroughly cleaned, begin by snapping chalk lines along the edge of the room to align the first row of panels. Lay the panels in place and cut around any obstacles such as cabinets, posts, or irregular walls, Figure 12-27. When all panels are properly placed, secure them using staples or screws according to the manufac- turer’s instructions. In some cases, panels must be secured with adhesive. Use blank pieces of plywood to fill any gaps in floor areas that are not being heated, such as under cabinets. Stagger end panels to avoid creating any “dead-end” circuits TECH TIP Using Insulated Floor Panels Some manufacturers offer an insulated floor panel system that provides an easily assembled, insulated modular board that includes a vapor barrier and radiant tube holding grid. This system simplifies installation of hydronic radiant floor heating systems in both slab-on-grade and above-grade installations, Figure 12-24. ANDREY-SHA74/Shutterstock.com Figure 12-24. Some manufacturers offer a floor panel system that provides an easily assembled modular board that includes a holding grid, as seen here. brizmaker/Shutterstock.com Figure 12-25. Once the tubing is in place, the concrete or gypsum underlayment material is now poured and finished. Flooring Subfloor Grooved panels Floor joist Uponor, Inc. Figure 12-26. Prefabricated radiant floor panels are designed to fit over an existing wooden subfloor.