How a Zone Valve Works


What are Zone Valves?

  • Zone valves are a specialized form of valve commonly found in home steam- or hot-water-based heating systems, typically referred to as hydronic systems. They rely on pipes running through the various rooms of the house to carry hot water from a central boiler, the heat radiating out into the room from the pipes. It would be a vast expenditure to keep a boiler supplying the entire house with heat, so most hydronic systems are sectioned off into zones. Whether a given room is heated is controlled by that room's zone valve.


  • There are two principle types of zone valve: one that is open in its inert state, and one that is closed in its inert state. There is no real physical difference, save that a different type of thermostat is used for each. The valve is a simple metal tube with a 24-volt electrically powered motor inside. The motor connects to the valve obstruction inside the tube by a simple mechanical linkage, and is held in its inert state by an attached spring. Inside the wall of the valve is a temperature sensor connecting to the temperature regulator in the hydronic system's boiler, called an aquastat. The thermostat connects to the motor, and from the motor is a wire connecting to the hydronic system's water pump. There is a separate thermostat for each room and zone valve.


  • When a thermostat is turned on in order to raise the temperature of the room, the thermostat either stops sending an electrical signal to the zone valve's motor or starts sending one dependent on the type of zone valve. In either case, the valve obstruction is turned to open the valve. Simultaneously, the motor sends a signal to the hydronic system's water pump to start pumping water from the boiler. As water passes through the valve, the boiler's level of heat is governed by feedback the aquastat receives from the valve.

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