Glossary – Block B: Heating and Cooling Systems

These use electric pumps, valves, and controllers to circulate water or other heat-transfer fluids through the collectors. There are three types: direct, indirect/ closed-loop, and drainback. (Section B-2.1)

A type of window or vent with slats that can be moved or tilted. These slats can be adjusted to control the amount of light, air, and noise that comes through, making them useful for ventilation and privacy. (Section B-3.1)

The process of removing trapped air from a hydronic heating system to ensure efficient operation. Usually accomplished using air vents placed at high points in the piping. (Section B-3.2)

(Also called air separators or air scoops); A device used in heating and cooling systems to remove larger air pockets and air bubbles from water, which can cause problems like noisy pipes or reduced efficiency. The device helps to keep the system running smoothly by ensuring that the water is free from air. Also see microbubble resorber. (Section B-4.1)

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, Section B-3.1 and Section B-3.2)

A device used in heating systems to control the temperature of the water. It works like a thermostat but specifically for water, turning the boiler on or off to keep the water at the desired temperature. (Section B-2.1)

An organization or person responsible for enforcing safety and building codes. They make sure that buildings and structures follow the law and safety standards, such as proper electrical wiring and fire safety measures. (Section B-2.2)

A device that stops water from flowing backward into the water supply. It ensures that water doesn't get contaminated by preventing dirty or used water from flowing back into clean water lines.  (Section B-4.2)

A valve used in a piping system to control and balance the flow of fluid to ensure that each part of the system gets the right amount of flow. It also helps to make sure that all sections of the system work efficiently and evenly. (Section B-4.3)

A valve that controls the flow of liquid using a ball with a hole through the center. When the ball is turned so that the hole lines up with the pipe, liquid flows through. When the ball is turned so that the hole is perpendicular to the pipe, the flow is blocked. Ball valves are known for their quick and easy on-off operation. (Section B-4.2)

Heating devices installed along the baseboards of rooms. They use electricity or hot water to produce heat, which is then radiated into the room. These units are effective for heating spaces efficiently and are often controlled by thermostats to maintain desired temperatures. (Section B-3.1)

A valve that allows water to quickly flow around a system or component. It is used to quickly fill up or bypass parts of the system, making it easier to manage and maintain. (Section B-4.2)

Water is contained in tanks called sections, with hot flue gases passing around the sections. (Section B-2.1)

The process where tiny bubbles or vapor pockets form in a liquid when the pressure drops below the liquid's vapor pressure. These bubbles can collapse suddenly, creating strong shockwaves and high temperatures. Cavitation can occur in pumps, propellers, and other machinery, and while it can be useful in some processes (like cleaning or mixing), it can also cause damage to equipment over time. See also cavitator.  (Section B-4.1)

A device used to create cavitation in a liquid. Cavitation happens when rapid changes in pressure cause tiny bubbles to form and then collapse. These collapsing bubbles can generate powerful forces that help mix, stir, or break down materials. Cavitators are used in various applications like cleaning, chemical processing, and in some industrial processes to improve efficiency. See also cavitation. (Section B-4.1)

A device that moves liquids by using a rotating impeller. The impeller spins the liquid outward through centrifugal force, pushing it through the pump and into the pipes of a system. Centrifugal pumps are commonly used in water supply, heating, and cooling systems to efficiently move fluids. (Section B-4.1)

A valve that allows liquid to flow in only one direction. It automatically closes when the liquid starts to flow backward, preventing backflow. Check valves are used to keep liquids from flowing the wrong way in a pipe system. (Section B-4.2)

A device that moves water through a heating or cooling system. It helps distribute hot or cold water to different parts of a building, ensuring even temperature control. Circulating pumps are essential for systems like radiators and underfloor heating. (Section B-4.1)

The process of shutting off or separating a specific part of a system, like a pipe or valve, from the rest of the system. This is done to allow for repairs or maintenance without affecting the entire system. It ensures that only the isolated part is affected while the rest continues to operate normally. (Section B-4.2)

The transfer of heat through direct contact between materials. Heat travels from warmer to cooler areas within an object or between two objects in contact. (Section B-1.1)

The transfer of heat through the movement of liquids or gases. Warmer particles rise, while cooler particles sink, creating a circular flow that distributes heat. (Section B-1.1)

A heating device that warms up a room by circulating air over a heated surface. The warm air rises and spreads through the room, while cooler air is drawn in to be heated. This process creates a continuous flow of warm air, making the room comfortable. (Section B-3.1)

A term used to describe a situation where two substances, such as fluids or gases, flow in opposite directions relative to each other. This arrangement maximizes the efficiency of heat or mass transfer between the substances by allowing the greatest temperature or concentration difference across the exchange interface. (Section B-1.2)

An electrical circuit that supplies power to only one specific piece of equipment or appliance, without sharing the circuit with other devices. (Section B-2.2)

In active systems, use pumps to circulate water through the collectors. These systems are appropriate in areas that do not freeze for long periods and do not have hard or acidic water. Systems that are installed in hard or acidic water conditions may not survive the “payback period” if care is not taken to address water chemistry. In off-grid situations where solar energy may be the only option, water chemistry must be considered. (Section B-2.1)

A piping system design where the water or fluid returns directly to the source or starting point after passing through each section of the system. This means that each section gets the same temperature fluid and helps in balancing the system evenly. (Section B-4.3)

A pipe fitting that splits the flow of a fluid into two separate paths. It looks like a "T" shape and allows part of the fluid to be redirected or sent to a different part of the system while the rest continues along the original path. (Section B-4.2)

In active systems, are direct systems that use pumps to circulate water through the collectors, then drain themselves automatically to prevent freezing. Because the water in the collector loop drains into a reservoir tank when the pumps stop, this is still a good system for colder climates and does not require antifreeze and a heat exchanger. (Section B-2.1)

The dry return is the portion of the return main located above the boiler water level. (Section B-1.2)

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 and Section B-4.2)

A special tank in a heating or cooling system that helps manage the pressure caused by changes in temperature. When the water heats up and expands, the expansion tank provides extra space for the water to go, so the system doesn't get too much pressure. (Section B-4.1)

A valve that controls the amount of water that enters a system and lowers the pressure to a safe level. It helps keep the water pressure steady and safe for the system.  (Section B-4.2)

Heated flue gases travel through tubes that are surrounded by the water in the boiler. (Section B-2.1)

Solar energy systems that consist of dark metal plates mounted on building walls or roofs. These plates absorb solar radiation, heating the air which is then circulated for heating purposes inside the building. They are a passive method of harnessing solar energy for space heating and ventilation. (Section B-2.1)

A plumbing fixture installed in the floor of a building, typically found in areas like basements, bathrooms, or utility rooms. Its purpose is to remove excess water and prevent flooding by directing water into the building's drainage system. (Section B-2.1)

The control of how much fluid flows through a pipe or system. It involves adjusting valves or other devices to manage the flow rate, pressure, or speed of the fluid. This helps ensure that the system works efficiently and that different parts of the system receive the correct amount of fluid. (Section B-4.2)

Heating units that use a fan or pump to circulate air or water through the convector. They are more powerful than gravity systems and can distribute heat more evenly throughout a room. These systems are often used in larger buildings or where rapid heating is required. (Section B-3.1)

Part of a system where friction losses occur due to the flow of fluid through pipes or other components. In systems where friction loops are managed, the aim is to reduce friction losses and improve efficiency. (Section B-4.3)

A type of valve that controls the flow of liquid by raising or lowering a gate or barrier inside the valve. When the gate is fully open, the flow of liquid is unimpeded. When the gate is closed, it blocks the flow completely. Gate valves are good for stopping or allowing flow but are not ideal for regulating flow. (Section B-4.2)

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)

A valve that controls the flow of liquid by moving a disc up and down inside the valve. This movement allows for precise control of the flow rate. Globe valves are often used when it's important to adjust or regulate the flow of liquid rather than just stopping or allowing it. (Section B-4.2)

Heating units that use natural convection to circulate warm air. They are typically placed near windows and walls where cold air enters. As the air near the heater warms, it rises, creating a convection current that circulates throughout the room.  (Section B-3.1)

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” 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)

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 is 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 and Section B-4.2)

Steam heating systems use convectors, cast-iron radiators, wall fin tubes, and similar heat-emitting units. (Section B-1.4 and Section B-3.1)

A device used to transfer heat between two fluids (liquids or gases) without them coming into direct contact. It facilitates the efficient exchange of thermal energy, commonly found in HVAC systems, refrigeration units, and industrial processes. (Section B-2.1)

Devices designed to transfer heat between two fluids or between a fluid and a solid surface. They facilitate the exchange of thermal energy without the fluids coming into direct contact with each other. They work by maximizing surface area contact between the fluids to efficiently transfer heat from a warmer fluid to a cooler one, or vice versa, depending on the application's requirements. (Section B-3.1)

The exhaust gases produced from combustion processes, such as those in furnaces, boilers, or industrial equipment. These gases are typically very hot and contain by-products of combustion such as carbon dioxide, water vapor, carbon monoxide, and other pollutants. Hot flue gases are often directed through flues or exhaust pipes to safely remove them from the combustion chamber or heating system. They may also be used in heat exchangers to recover some of their thermal energy before being vented to the atmosphere. (Section B-3.1)

A raised concrete platform on which mechanical equipment, such as a boiler, is mounted. (Section B-2.2)

A unit that uses circulating water to heat or cool air by passing it over coils, adjusting the room temperature efficiently. (Section B-3.1)

A system that uses water to heat a building. Water is heated in a boiler and then pumped through pipes to radiators or underfloor tubing. As the hot water moves through these pipes, it releases heat into the rooms, keeping them warm. (Section B-3.1)

A rotating part of a pump or other machine that moves fluid by spinning. It has blades that push the fluid outward from the center, creating flow and increasing pressure. Impellers are commonly found in devices like centrifugal pumps and are essential for moving liquids efficiently. (Section B-4.1)

The center part of an impeller where liquid or gas enters before being pushed out by the spinning blades. It's like the entrance point that leads the fluid into the impeller. (Section B-4.1)

In active systems, these pump heat-transfer fluids, such as a mixture of glycol and water, through collectors. Heat exchangers then transfer the heat from the fluid to the water within the heating system. These systems are used in climates subject to freezing. (Section B-2.1)

The amount of energy the boiler consumes in order to produce heat. (Section B-2.1)

A material that reduces the transfer of heat. It traps air or uses materials like foam or fiberglass to slow down heat loss or gain, helping to maintain comfortable temperatures in buildings. (Section B-1.1)

This type of passive solar watering heating system consists of one or more storage tanks placed in an insulated box with a glazed side facing the sun. During the winter, the connecting piping must be drained or protected from freezing. (Section 2.1)

The job of the low-water cut-off is to shut off the burner should the water level fall to an unsafe level. The boiler manufacturer determines this level, but it is usually within one-half inch of the bottom of the gauge glass. (Section B-1.2 and Section B-2.1)

A valve that controls the flow of water or other fluids into or out of a system. It can completely stop the flow when needed, allowing you to turn off the entire system or isolate it for repairs or maintenance. (Section B-4.2)

A device used in heating and cooling systems to remove very tiny air bubbles (microbubbles) from water that may not be captured by standard air purgers. By getting rid of the bubbles, the microbubble resorber may more efficiently help the system work better and more quietly. See also air purgers.  (Section B-4.1)

An outlet tapping is when a hole is made in a pipe to add another pipe or valve. This lets water or gas flow from the main pipe to a new area, like a faucet or another system. (Section B-1.2)

The amount of energy that is actually transferred to the medium being heated (water, heating fluid, glycol, etc.). (Section B-2.1)

A situation where two substances, such as fluids or gases, flow in the same direction relative to each other. In heat exchangers, parallel flow occurs when both the hot and cold fluids move in the same direction through adjacent channels or tubes. This configuration typically results in a lower temperature difference between the two fluids compared to counterflow, but it is simpler to construct and often more compact. (Section B-1.2)

Solar water heating systems that move water or heat-transfer fluid without pumps. There are two types of passive systems: Integral collector storage (ICS) and thermosiphon systems. (Section B-2.1)

A water supply system that provides water safe for drinking and other domestic uses, free from harmful contaminants. (Section B-2.2)

A graph that shows how well a pump can move water at different speeds. It helps us see how much water the pump can push out at different pressures or flows. (Section B-4.1)

Small connectors used in boilers and heating systems to join sections of piping together securely. They allow for easy assembly and disassembly when maintaining or repairing the system. (Section B-2.1)

Heating devices that are installed in ceilings, walls, or floors of buildings. They emit infrared radiation, which directly heats objects and people in the room without heating the air. This method of heating is efficient and provides comfortable warmth evenly throughout the space. (Section B-3.1)

The transfer of heat through electromagnetic waves. Unlike conduction and convection, radiation does not require a medium and can travel through vacuum, transferring heat from the Sun to Earth and between objects. (Section B-1.1)

Radiator valves control the steam supply to the system radiators. Each radiator is equipped with an angle pattern radiator supply valve. (Section B-1.2 and Section 4.2)

Heating devices that use hot water or steam to warm a room. They consist of metal panels or pipes that emit heat through radiation and convection. Radiators are commonly found under windows or along walls and are controlled by thermostats to maintain desired temperatures. (Section B-3.1)

These valves protect 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, Section B-4.1, and Section B-4.2)

The leftover warmth retained by an object or substance after the source of heat has been removed. It can be useful in conserving energy or maintaining temperatures in systems like engines or household appliances. (Section B-2.1)

A piping system design where the fluid flows in a way that the return path is the opposite of the supply path. This means that the last section to receive the fluid is the first to return it, helping to balance the system and ensure even heating or cooling throughout. (Section B-4.3)

A vertical pipe or duct that carries water, steam, air, or other fluids up through different floors of a building. It's used to move fluids between different levels or stories in a building. (Section B-1.2, Section B-4.1, and Section B-4.4)

A horizontal pipe or section of piping that extends from a riser to other parts of a system. It helps direct the flow of fluids from the vertical riser to different areas or equipment. (Section B-4.4)

A type of piping arrangement where the water or other fluid flows through one section of the system, then directly into the next section, like a chain. In a series loop, all the sections are connected in a single path, so the fluid passes through each one in order. (Section B-4.2)

A container where a mix of substances, like water and chemicals, is stored. It's used to hold and sometimes mix these substances before they are used in a process or system. (Section B-4.1)

A type of pipe or fitting that includes a spring to allow for movement or adjustment. It helps accommodate changes in temperature, pressure, or alignment in the piping system, reducing stress and preventing damage. (Section B-4.4)

A vertical pipe used to carry liquids or gases from one place to another. It’s often found in systems where a pipe needs to reach a higher level or where it helps manage the flow of liquids. (Section B-4.1)

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)

Note: Steam boilers differ from hot water boilers because they are only partially filled with water. They have a sight glass for checking the water level and a relief valve to prevent damage from excessive pressure. A pressure switch, or pressuretrol, controls the burner and determines the boiler's operating pressure. When heat is needed, the boiler runs until it reaches the pressuretrol's cut-out setting, then the pressuretrol shuts off the burner. Commercial boilers also have a manual-reset high-limit pressuretrol to turn off the burner if the pressure gets too high.

The 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)

A type of flexible pipe fitting that allows for movement and adjustment. It helps connect pipes or equipment while accommodating changes in position or alignment, making it easier to install and maintain the system. (Section B-4.4)

This type of passive solar watering heating system relies on convection created between the fluids in the tank and in the collector. The fluid in the collector becomes less dense and rises into the tank above, while the denser fluid in the bottom of the tank falls through piping into the bottom of the collector to be reheated. The fluid to be heated is circulated through a separate path within the tank (heat exchanger) where it absorbs the heat created and returns to the building for use. (Section B-2.1)

A process where a liquid moves naturally without the need for a pump, because of temperature differences. When a liquid gets heated, it becomes less dense and rises. Cooler, denser liquid then moves in to take its place. This creates a natural circulation of the liquid. It's often used in heating systems and solar water heaters. (Section B-4.3)

The process of controlling the flow of a fluid (liquid or gas) by partially obstructing or restricting the passage through a valve or other device. This adjustment allows for precise control over the flow rate, pressure, or speed of the fluid. Throttling is commonly used in various systems, like heating and cooling systems, engines, and pipelines, to manage the performance and efficiency of the system. (Section B-4.2)

A device that measures and displays three different things at once: pressure, temperature, and altitude (or level) of a liquid in a system. It's commonly used in heating systems to monitor these conditions and ensure everything is working properly. (Section B-2.1)

A way of moving water in a building where the water comes in from the bottom and gets pumped up to higher floors. This is often used in places where the water pressure isn’t strong enough to reach the top on its own. (Section B-4.3)

A device that controls the flow of fluid through a pipe by narrowing the pipe at a certain point. This narrowing causes the fluid to speed up and the pressure to drop. Venturis are often used to measure flow rates or to mix fluids. (Section B-4.3)

A spiral-shaped casing in a pump that surrounds the impeller. It helps direct the flow of liquid as it leaves the impeller, converting the high-velocity flow into a more controlled, higher-pressure flow. The volute design ensures efficient movement and pressure management of the liquid within the pump system. (Section B-4.1)

Energy that is produced but not used efficiently, often escaping as heat during processes like running machines or producing electricity. Instead of being used, this energy is usually lost to the environment. (Section 2.1)

The process of adding water to a system to replace water that has been lost due to evaporation, leakage, or other reasons. This is commonly done in systems like boilers, cooling towers, and HVAC systems to maintain the proper water levels and ensure the system operates efficiently. The added water is often treated or conditioned to match the quality and chemistry requirements of the system. The term "water makeup" is used to indicate the piping and accessories connected to the system that not only fills it but keeps a constant pressure within it. (Section B-4.2)

Water travels through tubes that are surrounded by the hot flue gases within the fire chamber. (Section B-2.1)

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 the dry return does. (Section B-1.2)

A valve used in heating or cooling systems to control the flow of fluid to different areas or zones of a building. It allows you to control the temperature in each zone separately, so you can heat or cool only the areas that need it. (Section B-4.4)