MEP Engineers Explain Why Hydronic Piping Is Used In Most HVAC Systems

HVAC installations are distinguished by a wide range of system configuration available. Also, many HVAC systems do not heat or cool the indoor air directly, but need a medium for the exchange of heat. The term “hydronic” refers to utilizing water or another fluid for moving the heat.

You might wonder, since the goal is to control the indoor air temperature, why is water used as a medium for heating and cooling? This article emphasizes on the performance advantages of hydronic HVAC systems over forced air systems. Some of the major advantages are:

  • Water has higher density and specific heat capacity than air, which means hydronic piping require less space than air ducts.
  • Blowing air to upper floor vertically is difficult, inefficient and impractical. Its much easier to pump the water through hydronic pipes.
  • Air ducts, along with the warm air, can carry and spread dust and harmful particles like mold, bacteria and viruses. Hydronic HVAC systems, on the other hand, have separate air handler for each area.

Now that you know a little bit about the performance advantages of hydronic HVAC system, let’s dive further into why hydronic piping is widely preferred.

Hydronic Piping is More Compact Than Air Ducts

The distribution system with hydronic piping requires less space for a given heating and cooling load. This can be elaborated with the physical properties of water and air:

  • Water has a density of 1000 kg/m3 and a specific heat capacity of 4.187KJ/kg-K.
  • Air has a density of 1.225kg/m3, specific heat capacity of 0.718KJ/kg-K at constant volume and 1KJ/kg-K at constant pressure.

From the above physical properties, we can see that, 1kg of water can carry almost 6x more heat than 1kg of air at constant volume. Also, 1kg of water needs over 800x less space than 1kg of air.

In simple terms, hydronic piping can reduce the space used by the building’s mechanical equipment, which is always beneficial for the building developers. The saved spaced can be utilized for other building systems or to expand the tenant space size.

Pumping Water Vertically is Simpler Than Blowing Air

Houses commonly use vertical ducts for the furnace in the basement, and the concept works properly since the vertical distance travelled by air is small, normally 1 or 2 floors. In case of buildings with high number of floors, vertical air ducts are not feasible and becomes less efficient.

In tall buildings that use air ducts, the air cannot be delivered effectively to the upper floors due to the high static pressure. At best, effective air distribution can be expected in the bottom floor levels. Thus, in tall buildings, hydronic pipes coupled with water pumps are much more effective and efficient for distributing the heating or cooling of air to all the floors.

To further optimize the heating or cooling requirement, the combination of vertical hydronic piping and air handlers for each floor is one of the most efficient HVAC option for tall buildings. In such cases, there are mainly 2 types of piping configurations:

  • 2 Pipe System: It has only one water loop, meaning all the air handlers must be either in heating or cooling more.
  • 4 Pipe System: It has 2 water loops, which allows independent operation of air handlers. This means some building areas can have heat while the others are being cooled.

Hydronic Piping Systems Are Better for Health

When air ducts cover the entire building, air pollutants and unpleasant odors can spread easily to multiple areas in the building. On the other hand, buildings with hydronic HVAC system have independent air handlers for building areas. This allow better control over isolating and dealing with the harmful air pollutants, dust and odors.

Hydronics HVAC systems can also be designed to be embedded in the walls and ceilings. In such cases they are called as radiant systems. The heating and cooling requirement is directly delivered through the walls and floors without needing an interaction with the ventilation system. Radiant HVAC systems are silent and have zero chance of spreading air pollutants.


Hydronic HVAC systems can offer a lot of advantages are considered to be ideal for tall buildings. For identifying the best possible settings, it is recommended to consult with a MEP engineering team that can specify your installations. For instance, hydronic HVAC systems can be expensive for small residential projects, and a centralized hydronic HVAC system may not be suitable for building areas with independent schedules.