Hydronic Heating and Cooling Piping
This domain tests hydronic piping and components: expansion control, relief valves, air elimination, backflow protection, pipe materials, supports, freeze protection, boiler trim, controls, and radiant systems.
Core rules
- Closed hydronic systems need expansion tanks sized for system volume and temperature change. The tank precharge and system fill pressure must be coordinated so air is not drawn in or relief valves do not weep.
- Pressure relief valves must protect the boiler or vessel, be set at or below the equipment rating, and have a discharge pipe that is not trapped, reduced, capped, or obstructed. Discharge must terminate safely.
- Air elimination is required at high points and near equipment. Piping must be supported, protected from freezing, and arranged to avoid trapped air and dead legs.
- Backflow protection is required where makeup water can contaminate the potable supply. Boiler trim, low-water protection, and controls must remain functional.
- Radiant and snow-melt systems need careful zoning, temperature control, and freeze protection; glycol systems require compatible components and correct concentration.
Worked example
A boiler relief valve is set at 30 psi, but the installer routes the discharge through a 1/2 in pipe, caps the end to stop dripping, and traps the line. This fails: the discharge must remain full size, untrapped, uncapped, and terminate safely. A dripping relief valve indicates a system or expansion-tank problem, not a reason to plug the pipe.
Traps
Capping or reducing relief discharge; mismatching expansion-tank precharge and fill pressure; omitting air vents; using incompatible materials in glycol systems; and failing to protect piping from freezing.