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What Is a Hydronic HVAC System Anyway?

Picture of Joe Britt, PE
By Joe Britt, PE on November, 13 2015

Raypak_XThermAre you unfamiliar with how air conditioning, or HVAC, systems work? HVAC is the Heating, Ventilating, and Air Conditioning (HVAC) method for conditioning the indoor environment of a building, usually with the intent of keeping the occupant comfortable. A hydronic HVAC system utilizes water as the primary fluid to transfer energy throughout the building. Water has outstanding heat transfer characteristics, along with other benefits (i.e. – plentiful, non-toxic, “green," inexpensive) that make it ideal for this purpose.

To deliver heat, the system must have a heat source, such as a boiler, and to provide cooling, the system must have a cooling source, such as a chiller or cooling tower. The heated or cooled water is pumped throughout the building to air handling units or terminal units (or other similar), where it transfers energy with air from the ventilation system before it recirculates to the heating or cooling source. The conditioned air is then delivered to the room.

Of course, this is an oversimplification, as there are a number of variations of hydronic HVAC systems, such as geothermal heat pump systems, radiant heating & cooling systems, fan coil, VAV, four-pipe, two-pipe, and so on. Just to give you a basic understanding, I would like to use an analogy, if I may.

Imagine a large building (such as a school) is like the human body. It has different parts that must be heated or cooled (hot head, cold feet, etc.). The water in the HVAC system is similar to the blood in your body – it is the component that transports energy from one area to another. Water is circulated with pumps, just as the heart circulates blood. Without circulation, the system dies! The boiler (stomach or digestive system) converts fuel (food) such as natural gas into energy. The air handling system (lungs, or respiratory system) provides proper fresh air and ventilation. I could carry the analogy further, but does this help paint the picture?

So, a building may be viewed as a large “body” with a mechanical system designed to keep “human” bodies comfortable. At Heat Transfer Sales, we like to think of ourselves as similar to a “medical specialist”, the one you turn to when you need a high level of expertise in one specific field. For us, that field includes the application of equipment related to the heating, cooling, or circulation of water in a Hydronic HVAC system.

And in a nutshell, that is what a hydronic HVAC system is.  Stay tuned for more general knowledge posts!


There are many pieces to a hydronic HVAC system.  Click on the link below to find out more about condensing boiler systems.

Condensing Boiler  Systems

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