B-1 Types of Heating and Cooling Systems Introduction

The following terms will be used throughout this section. A complete list of terms for this section can be found in the Glossary.

• air vents: Steam cannot circulate, nor can radiators emit heat until air has been vented from the system. Thermostatic air vents are installed on each radiator and at the end of each steam main. Thermostatic steam traps also act as air vents. (Section B-1.1)
• dry return: The portion of the return main located above the boiler water level. (Section B-1.2)
• equalizer line: The vertical piping at the end of the header going back to the boiler return connection. Its job is to return any water that slips out of the boiler with the steam and to balance the pressure between the supply and the return sides of the boiler. Without a properly sized equalizer, water can back out of the boiler. (Section B-1.2)
• gauge glass: Used to identify the water level in the boiler. Expect to see some minor movement in the water line when the boiler is operating. When the boiler is off, the “normal” water line is the centre of the gauge glass. When the system is running, the “normal” water line is near the bottom of the gauge glass. (Section B-1.2)
• Hartford loop: A piping arrangement designed to prevent complete drainage of the boiler if a leak develops in the wet return. The wet return is connected to an equalizing line between the supply and return opening of the boiler. This connection is made about 2 in. below the normal water level of the boiler. This connection between the loop and the equalizer must be made with a close nipple to prevent water hammer. (Section B-1.2)
• header: Boilers, depending upon their size, have one or more outlet tappings. The vertical steam piping from the tapped outlet joins a horizontal pipe called a “header.” The steam supply mains are connected to this header. If the boiler has more than one outlet, it’s important to remember to pipe the headers with swing joints. This will help alleviate any stress on the boiler when the header heats up and expands. (Section B-1.2)
• heat emitters (units): Steam heating systems use convectors, cast-iron radiators, wall fin tubes, and similar heat-emitting units. (Section B-1.4)
• low-water cutoff: Shuts off the burner should the water level fall to an unsafe level. The boiler manufacturer determines this level, but it’s usually within one-half inch of the bottom of the gauge glass.
• radiator valve: Controls the steam supply to the system radiators. Each radiator is equipped with an angle pattern radiator supply valve. (Section B-1.2)
• relief valve: Protects the boiler against a runaway fire. On space-heating steam boilers, the relief valve is set to pop open and relieve pressure at 15 psi. This is the limit for any low-pressure boiler. (Section B-1.2)
• risers: The vertical pipe carrying steam to the radiator from the supply main. (Section B-1.2)
• steam boiler: A steam boiler is a device that heats water until it turns into steam. This steam is then used to provide heat or power. It works by burning fuel like coal, oil, or gas, or by using electricity to generate heat. The steam produced can be used for various purposes, such as heating buildings, running engines, or powering machines. (Section B-1.2)
• steam supply main: Carries steam from the header to the radiators connected along its length. (Section B-1.2)
• steam traps: Prevent steam from getting into the condensate returns because they close in the presence of steam, creating a separation from the return piping of the system. The steam trap has three jobs — to let air pass through the radiators, to close when steam reaches it, and to open when condensate accumulates. (Section B-1.2)
• wet return: The portion of the return main located below the boiler water level. It is always completely filled with water and does not carry air or steam in the same way that the dry return does. (Section B-1.2)