Copyright Goodheart-Willcox Co., Inc. 248 Hydronic Heating: Systems and Applications if the concrete slab is not properly insulated. Two types of insulation are available: expanded foam board (EPS) and extruded foam board (XPS). Both are popular choices for thick slab insulation. However, extruded foam board will lose up to 50% of its R-value over its lifetime therefore, expanded foam board is a better choice. Typically, a 2″ layer will be sufficient, but be sure that the insulation used has a minimum R-value of 5 and check with local building codes for the proper amount of insulation for your area. Be sure to properly insulate the perimeter with edge insulation and cover any exposed foundation walls. Do not insulate areas that will be under support columns or bearing walls. 3. Reinforce the slab. Lay down either welded wire fabric (WWF) or steel reinforcement bar (rebar). The tubing can be attached to the WWF or rebar to hold it in place while the concrete is poured, Figure 12-19. 4. Roll out the tubing. Uncoil the rolls of tubing and lay out the individual loops onto the WWF or rebar. There are several different tubing layout patterns to choose from, depending on the amount of heat loss in a given zone, Figure 12-20. Zones with the greatest heat loss will have the tightest layout pattern. It is a good idea to mark the tubing layout patterns along the floor with spray paint before rolling out the tubing. Also, be sure to mark which ends of the tubing are supply and return so there is no confusion when connecting these ends to the manifold station. 5. Fasten the tubing. Connect the tubing to the reinforcement fabric using nylon cable ties, metal twist ties, or plastic clips, Figure 12-21. Space the fasteners a minimum of 3′ apart along straight runs, and every 12″ along bends and arcs. Be careful not to puncture the tubing with any sharp edges along the slab’s reinforced wire fabric or rebar. TECH TIP WWF: Sheets versus Rolled Fabric If using welded wire fabric, sheets are recommended over rolled fabric. Sheets are noticeably easier to install and provide a flatter surface. The only downside is that the sheets will need to be tied together. Wolfgang Filser/Shutterstock.com Figure 12-20. Tubing patterns will vary according to the amount of heat loss in a given zone. nikkytok/Shutterstock.com Figure 12-19. Once the insulation is installed, reinforce the cement slab with either rebar or welded wire fabric (shown here). Rigamondis/Shutterstock.com C A B tchara/Shutterstock.com