Watts News
 Published for the members of North Itasca Electric Cooperative
VOL. 24 NO. 5  -  May 2020

Radiant heat vs. forced air heating systems


The picture below shows a forced air system and by following the arrows (which represent air movement), you will see that the warmest air coming from your furnace is distributed to the room by heat registers located on the outside or exterior walls.

From science class we have learned about air molecules. Air molecules (when heated) become lighter. When our furnaces heat up these air molecules, they become much lighter than the air in our home and begin to rise. When following the arrows shown in the picture, we can see that the warmest air from the register begins to rise upward toward the ceiling. If you also remember from science class that heat always seeks after cold, as you continue following the arrows, the temperature of the air begins to fall as it travels along the outside or exterior wall from a discharge temperature of 110 degrees from the register, to 100 degrees along the exterior wall.

The cold winter air temperature is pulling the heated indoor air temperature toward itself and already the room has lost 10 degrees in heat loss. The heated air molecules (even though cooled down), are still lighter than the indoor air of your home andcontinue to rise until hey reach the ceiling. As the exterior wall pulls heat from the room, it does the same to the cold air above your home or attic. We call this heat loss conduction loss.

It is like laying on a cold floor where the heat of your body is transferred to the cold floor or being in the freezer section of a grocery store when it feels cooler but is not. The cold freezer is pulling the heat from your body making you feel cold.

As time passes, the heat within these molecules continues to decrease and become heavier, and they lose ability to rise as they are being replaced with warmer molecules forcing them now downwards. We can see in the picture this cooler air descending back to the floor until pulled in by the return register to be reheated again by the furnace.

In summary, the air temperature is always changing within the home being reheated and circulated by a furnace fan motor. Inside and outside walls are different temperatures and comfort levels change.

Now let us look at a radiant heating system.

There is no ductwork to distribute heated air molecules. The floor is heated by water tubes or electric wires below or within the floor heating it up.

Remember heat seeks after cold? Here the heat within the warm floor is pulled in by the colder objects within the home: walls, furniture and yes, people. Since the floor is warmer than the objects in the home, (opposite to when in the freezer section of a grocery store), the objects in the home pull heat from the floor drawing, it into themselves. Radiant heat does not heat air molecules; thus, this heat does not rise to the ceiling where there is no need for warmer air to be. Radiant heat functions like the sun as it heats the earth. When we stand in the sunlight, we can feel the sun’s rays upon us. These rays are not heating the air but objects. Otherwise, outer space itself would be hot.

There are other advantages to radiant heat. Warm air is not moving around drying out furniture, humidifiers aren’t needed to bring moisture levels up, less heat is needed because hot air is not rising to the ceiling, there are no noisy furnace blowers, the heat is constant and comfortable with no noisy equipment operating, one’s feet are always warm, (when our feet are warm, than we will be warm) and all temperatures within the home will have a constant temperature.

Now we know some basic differences between radiant and forced air systems.