CSLB C-20 HVAC ContractorHeating SystemsEasy
A hydronic baseboard heating system has multiple zones, each controlled independently. What component allows one zone's thermostat to call for heat without activating water flow to the other zones?
- AAn aquastat mounted on the boiler
- BZone valves (or zone circulators) controlled by individual thermostats
- CA mixing valve at the boiler supply
- DA single common circulator pump for all zones
Show answer & explanationAnswer & explanation
Correct answer: B. Zone valves (or zone circulators) controlled by individual thermostats
Independent zone control in hydronic systems is achieved using zone valves (motorized valves that open/close per thermostat call) or dedicated zone circulator pumps, directing flow only to the calling zone.
Why the other options are wrong
- A. An aquastat controls boiler water temperature, not zone flow distribution.
- C. Mixing valves blend supply/return water temperature, not zone isolation.
- D. A single shared pump alone cannot isolate flow to individual zones without valves.
Hydronic Zoning
Method of dividing a hydronic system into independently controlled areas using zone valves or zone circulators triggered by individual thermostats.
- Zone valves are motorized and open/close based on thermostat calls
- Some systems use a dedicated circulator per zone instead of valves
- End switches on zone valves signal the boiler/circulator to run
Memory trick: One thermostat, one valve, one warm room — others stay closed till their turn.