How does radiant heat save energy?

Tue, 01/21/2014 - 10:13

A typical radiant heated home in the US can expect a 25%* energy savings over a conventional forced air home due to a variety of factors that are explained below. This savings can be further increased if using high efficiency heat sources in conjunction with the radiant heat system.
* 1998 study by Kansas State University and the American Society of Heating Refrigeration and Air-Conditioning Engineers [ASHRAE])

Parasitic losses
Parasitic loss refers to energy lost due to inherent inefficiencies of a system. Duct work in a forced air heating system, for example, can be difficult to permanently seal/insulate and is often located in unheated crawl spaces or basements. As hot air is blown through these large ducts, heat is lost through the tiny flaws in the system and escapes into unknown areas.

Additionally, when hot air is blown into a room with a door closed, it can cause an increase in air pressure. This pressure pushes the heat through weather stripping on windows. Blowers used in forced air systems on average require 9x the amount of electricity as the pumps in radiant systems. All of these parasitic losses add up in forced air systems to a 30% less efficient system.

Lower ceiling temperatures
Forced air systems emit hot air at a temperature of approximately 120–140 degrees Fahrenheit. This hot air rapidly rises, creating a temperature zone that can often be over 10 degrees warmer than the air below. This stratification effect becomes greater as the ceiling height increases. In addition, when ceilings are hot and just below a cold roof, heat loss is quite high. It is precisely because of this effect that we insulate ceilings and attics so much.

Zoning reduces energy usage
Most forced air homes have a single thermostat. In other words, they are single zone systems. This is because forced air systems are inherently difficult and therefore, expensive to zone. The result is a top story that's too hot, while downstairs remains cool. Or rooms facing direct sunlight become overheated while other rooms are inadequately controlled.

Lower air temperatures for the same comfort
When we are outside on a warm, sunny day, we may be comfortable in a tee shirt even if the air is only 60 degrees. This is because the radiant warmth from the sun allows us to be comfortable at a lower air temperature. The same is true in your home. With the warmth emanating from a radiant floor, we can experience the same level of comfort with the thermostat set a few degrees lower than needed in a forced air home.

Blowing hot air paradoxically can cool us
We can be quite comfortable outside until the wind picks up. Even though the temperature has not changed, the movement of air across our skins causes evaporative cooling. Paradoxically, hot air blowing from a duct may require you to set the thermostat slightly higher to maintain the same comfort.

All of these aspects contribute to the inherent efficiency, and energy savings, of radiant heating when compared to forced air. Coupled with the many other benefits of radiant heat, there really is no comparison.