Boiler Systems (Strand 5): Hydronic and Steam Heating—Operation, Safety, and Service

Boiler System

Heats water to move thermal energy into a building.

Hydronic System

A hot-water heating system where water is circulated in a closed loop to deliver heat.

Steam System

A heating system that boils water to send steam into distribution piping.

Heat Exchanger

A device that transfers heat between two or more fluids without mixing them.

Aquastat

A temperature-sensing control that manages the temperature in a hydronic system.

Circulator Pump

A pump that moves hot water through piping in a hydronic heating system.

Expansion Tank

A tank that absorbs water volume changes due to heating in a closed hydronic loop.

Pressure Relief Valve

A safety device that opens to release pressure when it exceeds a certain limit.

Condensate

Water formed from steam as it cools and loses heat.

Low-Water Cutoff (LWCO)

A critical safety device in steam boilers that stops the burner if water level drops too low.

Zone Control

Mechanism used in hydronic heating to independently control temperature in different areas.

Steam Trap

A device that allows condensate to exit while preventing steam from escaping in steam systems.

Venting

The process of removing trapped air from a heating system to allow steam to enter.

Radiator

A device designed to emit heat from a heating system into a space.

Heating Emitter

Any device that releases heat from a heating system, such as radiators or baseboards.

Condensate Return

The system used to return condensate back to the boiler in a steam heating system.

Gauge Glass

A device that provides a visible indication of the water level in a steam boiler.

Combustion Control

Safety features in fuel-fired boilers that manage ignition and flame presence.

Boiling/Condensation Behavior

The phase change processes in a steam system that influence heating and pressure.

Air Removal Device

Components designed to eliminate air from hydronic systems to ensure efficient operation.

Distribution System

Network of pipes that carries heated fluid (water or steam) to emitters.

Thermostat

A device that signals the heating system to turn on or off based on temperature settings.

Flow Path

The designated route that heated water or steam travels in a heating system.

Control Strategies

Methods used to manage temperature and pressure in both hydronic and steam heating systems.

Makeup Water

Water added to a heating system to replace lost water, often indicating a leak if frequent.

Soot and Scale

Deposits that build up on heat-transfer surfaces, affecting efficiency and performance.