Copyright Goodheart-Willcox Co., Inc. 237 Learning Objectives After completing this chapter, you will be able to: ■ ■ Compare radiant heating systems to conventional heating systems and explain how they are different. ■ ■■ Describe how radiant heating relates to human comfort. ■■ Summarize the difference between high-mass and low-mass radiation. ■■ Compare various heating sources for radiant systems. ■ Describe the differences between various types of radiant piping materials, including the different types of PEX, PEX-AL-PEX, and PE-RT tubing. ■ ■■ Explain where PEX tubing with an oxygen barrier is required. ■ Compare the various piping configurations that are available for radiant floor heating. ■ ■■ Explain the procedure for installing slab-on-grade radiant floor systems. ■ Identify how concrete or gypsum thin-slab floor systems differ from slab-on- grade systems. ■ ■■ Describe the process for installing a thin-slab floor heating system. ■ List the types of radiant flooring systems that are available for both above- and below-floor applications and explain how they are designed and installed. ■ ■ Describe how radiant wall and ceiling panels function and list their installation steps. ■ ■■ Demonstrate design concepts for radiant heating systems. ■■ Explain how radiant heating systems are controlled. ■ List the different applications where snow and ice melt systems may be used and their installation steps. Technical Terms below-floor suspended tubing buffer tank coefficient of performance diffusion dry radiant hydronic system expanded foam board (EPS) extruded foam board (XPS) geothermal heat pump high-mass radiant system ideal heating curve low-mass radiant system manifold station oxygen barrier PE-RT tubing PEX-AL-PEX PEX (crosslinked polyethylene) prefabricated radiant floor panel radiant heating system radiant ceiling panel radiant wall panel slab-on-grade radiant piping socket fusion solar thermal storage snow and ice melt system thermal memory thin-slab radiant flooring system water-to-water heat pump wet radiant hydronic system vapor barrier U p to this point, our discussions have focused on conventional hydronic heating systems and the terminal devices typically used with them. In this chapter, we discuss radiant heating systems in detail and how they compare to conventional hydronic heating systems. A radiant heating system is one in which thermal radiation is used to transfer heat from the piping to objects in the space to be heated, rather than the air. We will cover the main principles of radiant heating, different methods of installation, types of piping and controls, and various applications for radiant systems. 12.1 Principles of Using Radiant Heating In previous chapters, we discussed how heat travels from warm to cold. Further- more, heat travels in three different ways: through convection, conduction, and radiation. With most conventional hydronic heating systems, heat actually is transferred by all three methods. For instance, heat from the burner inside the boiler comes in contact with the water-filled heat exchanger, which is a form of heat transfer by conduction. When the heat from the hot water inside the hydronic piping gives up its heat into the air, there is heat transfer by convec- tion. However, with radiant heat transfer, heat is conveyed in a direct physical path and heats the objects in the conditioned space, not the air. This is the main difference with heating by radiation rather than by conduction or convection. Another main difference between conventional hydronic heating systems and radiant heating systems is that in radiant systems the piping is considered the terminal device and is usually enclosed within walls, floors, and sometimes