Product Focus: Radiant Heating Systems Issue: 9/01 Terra Therma radiant floor heating systems from Slant/Fin offer superior PEX tubing and easy to control manifolds and controls. With the Terra Therma manifold assembly, its simple to balance the flow of heated water. A built-in balancing valve on each return module, plus provision for a manifold zone valve operator on each supply module, allow the heating system to be fine tuned loop by loop. To speed system set-up, pre-calculated zone settings may be determined with Slant/Fin system design software. Slant/Fin.