Understanding Hydronic Piping Systems

Hydronic systems circulate chilled or heated water through connections between pipes and terminal heat-transfer units made in a series of loops. A hydronic system can be configured as a two-pipe or four-pipe system and can supply chilled water to cool the building in the winter and hot water to heat it during the summer. Some two-pipe systems also have a common return pipe that returns hot and cold water, so the energy used to reheat or chill the water is reduced by cycling it back through the same system multiple times. 

Water Heater 

The water heater is a fundamental component of hydronic heating and cooling systems as it heats domestic hot water with a boiler or by using an indirect-fired tankless unit. The hot water circulates through piping that delivers it to radiant tubing or to baseboard heaters, radiators, and convectors throughout the building. This type of heating system does not require fans or vents to move air, so it’s very quiet and efficient. 


The radiator, a key component of the cooling system in your car, cools the antifreeze-water mixture that passes through passageways in the engine. The cooled liquid is fed back to the engine, and the cycle repeats. Most modern radiators have internal fins that greatly increase the contact surface of the tubes with air. This allows the exchange of heat between air and water to be more efficient. And while radiators come in different shapes, sizes, and designs, their basic function typically remains the same. 

Heat Emitters 

In a hydronic system, heated water travels through the piping to radiators and other heat emitters throughout the house. These include finned-tube baseboards, panel radiators, kickspace heaters, and radiant floors. All heat emitters require a specific supply water temperature to operate. When loads are connected in series, this should be calculated and used to determine the supply water temperature available to the next load along the circuit. The flow rate of the hot water through a heat emitter can also be fully controlled by a manual or automatic control valve located in the branch piping path. This allows for room-by-room zone control. 


There are many types of controls that can be installed with hydronic piping systems. They include pumps, coils, valves, and more. Some of these controls are designed to control the flow rate of water through a system’s piping, while others are used to control coils and heat exchangers. The right type of control can make a big difference in the performance and efficiency of a system. Some of the most common controls are Equal Percentage Valves, which allow for a certain percentage of the system’s total flow rate to be changed at any point in time. These are ideal for controlling the flow of water through coils and heat exchangers. 

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