Hydronic Controls

Systems must have controls to sequence boiler operation. If the system only has one boiler and is larger than 500,000 Btu/h, it must have either a multistaged or modulating burner.

Three-pipe systems are not allowed.

Two-pipe changeover systems must:

• allow a dead band between changeover of at least 15°F outside air temperature,
• have controls that allow operation in one mode for at least 4 hours before changeover, and
• have controls that allow heating and cooling supply temperatures at changeover point to be no more than 30°F apart.