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How Hydronic Radiant Systems Differ from HVAC Forced-Air Systems

Updated: Nov 1, 2021

HVAC companies offer traditional forced air units for heating and cooling. Hydronic radiant heating companies—like Warm Corp West—offer hydronic radiant heating and cooling systems.

Hydronic radiant heating differs from forced air heating in several ways. Two of the most important distinctions are the mode of heat transfer (convection versus radiation) and the medium used to convey that heat (air versus water).

It is a common misconception that “heat rises.” This is inaccurate. In fact, heated air rises. Hot air rises because, as it is heated, it becomes less dense than the colder air around it and therefore more buoyant. Heat itself, however, can be transferred in any direction, depending on the mode of transfer. Understanding this basic principle is important in understanding the distinction between forced-air and radiant technology.

How do forced-air units work?

Forced air units utilize a convection method of heat transfer, pulling in cold air, passing it over a heated element, and then circulating this heated air back out to a space. The heated air rises, pushing colder, more dense air down, which is again pulled into the forced air system. This is what is known as a convection current; and, unless you’re cake batter, it is very uncomfortable to sit in.

So how do hydronic radiant systems differ?

Hydronic radiant systems utilize the superior heat absorption abilities of water (when compared to air) to radiate heat from pipes in the floor or ceiling out to the objects within a conditioned space.

A prime example of radiant heat is the relationship between the Sun and the Earth. The sun emits radiant energy that passes through space and is absorbed by the Earth.

All objects either radiate heat or absorb heat based on their relative temperatures.

The primary effect of radiant heat transfer is that it heats objects as opposed to air. As illustrated in this example, the space between the sun and Earth is not heated—the Earth is. All objects either radiate heat or absorb radiant heat based on their relative temperatures. Apply this concept to a comfort conditioning system—like Warm Floors—and you can see that the warm water running through the pipes will radiate heat outward, first to the floor, and then beyond to other objects, raising the overall temperature of the space.

This radiant heat transfer process can be used in reverse when cool water is pumped through pipes and it absorbs first the heat from the floor or ceiling and then the heat from the rest of the objects in the room, reducing the overall temperature of the space. This is the basic process behind the Cool Ceilings system.

All in all, radiant heat transfer feels entirely different than convection heat transfer. And using water allows for a coefficient of performance (COP) in hydronic radiant systems that, due to its basic physical properties, air could never achieve. By circulating warm or cool water through concealed pipes, hydronic radiant systems can heat or cool a space with efficiency and comfort unparalleled by forced air alternatives.


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