The Glitch

Overview: A manually set three-way mixing valve was installed to regulate the supply temperature to the concrete-slab radiant floor system. A bypass valve is also installed to help boost the boiler inlet temperature.

Exercise: Assume the system undergoes a few modest nighttime setback periods as it operates through the heating season. What are the problems with this design?

The Fix

One of the problems with the design is the boiler is still not “guaranteed” to be protected against flue gas condensation. A high-mass slab can easily absorb heat from the water faster than the boiler can reproduce that heat by burning fuel. When this happens, neither the manually set 3-way valve nor the bypass will prevent the boiler temperature from dropping "

Links

• The Glitch & The Fix - March 2008