Radiant heat is more efficient than forced air

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Radiant heating practitioners and advocates have long said that radiant heating is more efficient than forced air. The consulting firm reported this last January that annual energy savings of up to 18% could be realized with radiant heat. In existing homes, built before 1980, national averages revealed energy savings of 12%. In U.S. dollars, the savings range from a low of $36.24 to as much as $210.16.

Radiant heating practitioners and advocates have long said that radiant heating is more efficient than forced air. The claim was based on common sense: If you heat up water to a maximum of 120°F with a condensing boiler in order to heat a radiant surface to a maximum of 85°F, coupled with the fact that hydronic heating is easily zoned, it only goes to reason that radiant is more efficient. What was lacking was data. The radiant heating industry has that data now thanks to its Canadian friends from Beautiful Heat.

Beautiful Heat is a non-profit joint venture of all of the interested parties in the Canadian hydronic heating industry to promote hydronics and radiant across the provinces. It has two things going for it that the U.S. industry has never been able to get together — a funding mechanism with which everyone could agree and a Canadian population that’s one-tenth that of the U.S. But that’s another story.

Beautiful Heat hired Ottowa, Ontario-based consulting firm ICF Marbek in 2013 to study and quantify the energy benefits of radiant heat. In 2011, consulting firm ICF International, Fairfax, Va., bought Marbek, which is one of Canada’s top environmental and energy management consulting firms.  

Based on the results from energy simulations of different home types, in six regions of Canada, ICF Marbek reported this last January that annual energy savings of up to 18% could be realized with radiant heat.

“Anecdotally we have had homeowners tell us that radiant heat has saved them as much as 30% to 40% on their annual heating bills,” said Simon Fedema, chairman of Beautiful Heat. (Fedema is also president of Grundfos Canada.) “As with any home, setting an ideal temperature is the domain of the owners and personal comfort levels can fluctuate greatly. With this study, we have modeled the dominant styles of homes and local climates in key regions across Canada to establish a national average that represents the baseline energy savings Canadians can realize with the installation of radiant heat.”

In existing homes, built before 1980, national averages revealed energy savings of 12% (16.6 GigaJoule) and 5% (4.1 GJ) in two-story and single-story homes respectively. ICF Marbek reported that savings of 10% (10GJ) and 5% (3GJ) could be realized in new homes. As a point of comparison, a GigaJoule is equivalent to about 948,000 Btu, so 10 GJ is 9.48 million Btu, and so on. Translated into annual dollar savings, new homes could range from of C$40 - C$136 and existing homes from C$54 to C$232. In U.S. dollars, the savings range from a low of $36.24 to as much as $210.16.

When multi-zone controls were enabled with a 2°F setback in basements and living rooms overnight and in bedrooms during the day, savings increased to an average energy of 10.6% in new two-story homes and 12.4% percent in existing homes. With a more aggressive 7°F reduction, energy savings in new housing grew to 15.1% and 17.0% in existing homes.

The radiant heating industry has also preached the comfort message because of the lack of stratification that results from even radiant heating of surfaces. Consequently, in addition to energy savings, ICF Marbek decided to estimate the average temperature reduction that could be realized through the consistent temperature that is provided by radiant heating without sacrificing occupant comfort. The firm found that to maintain an ideal heating setpoint temperature, which provides the same level of comfort in single-story homes, owners could set their thermostats an average of 4°F lower in new and existing structures. In two-story homes, that number increased to 5.6°F in both new and existing structures.

All houses were modeled with single HVAC zone, assuming that the entire house will be controlled by a single, constant cooling and heating setpoint schedule. For zone controls, Marbek modeled the new and existing two-story homes in Edmonton and Toronto with three HVAC zones to examine the impact of radiant heating multi-zone systems. The three HVAC zones were basement, living area (first floor), and bedroom area (second floor). “Living” and “Basement” zones were modeled with a night setback. “Bedrooms” zone was modeled with daytime setback.

So there you have it radiant industry. Go sell it.

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Robert Mader

Bob Mader is the editor of CONTRACTOR magazine, Green Mechanical Contractor magazine, and Radiant Living magazine. He has been writing about plumbing, mechanical, green building and HVACR topics for...
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