CPVC pipe is rated to 210F. After that it loses its shape. I have yet to hear of a successfully installed poured radiant system with CPVC pipe inside the pour. The labor to secure, glue fittings, and repair leaks make installation more difficult than other materials. CPVC may be used by some installers as manifolds and exposed pipe when temperatures are lowered to 160F. The usual plastic used for radiant is PEX today.
Likewise some systems use Pex as it can take 240F, although few hot water heating systems are used higher than 180F.
If you want a complete heating system, use a complete system designed by a radiant heating manufacturer. Weil McLain and other manufacturers will provide an entire factory-warranteed package installed by a qualified representative. http://www.radiantdesigninstitute.com/page2.html http://www.radiantpanelassociation.org/