How effective are water heaters for radiant heating? That seems to be a hot topic in the Radiant Panel Association (RPA), according to John Carpenter, territorial heating manager for D&C Plumbing & Heating Supply, Inc., Ann Arbor, MI.

“Radiant applications using water heaters have proven to be very effective,” Carpenter said.

Carpenter has been successfully selling hydronic system components to the trades. “A lot of guys haven’t used water heater hydronic systems. They weren’t sure that installing them would meet the codes,” he said.

“They assumed because hydronic systems worked with lower temperatures, they wouldn’t work as well [with water heaters].”

He added that when the water heater is used properly for an application, safety measures are ensured.

“Make sure that certain hydronic specialties are included, e.g., release valves, expansion tanks,” he said. “[These] backflow preventors need to be used with a water heater.”

He stated that the use of boilers is more common than the use of radiant water heaters. Accordingly, most hot water hydronic systems use a boiler, but most hydronic systems don’t boil. A true boiler is a steam boiler, he added.

Carpenter stated that the temperature the boiler produces is between 140° and 200°F. The boiling point of water is 212°F (or 100°C) at normal atmospheric pressure.

Carpenter explained that using a water heater, which produces a temperature of 120°F, delivers an average of 25 Btu/sq ft of floor panel surface. Floor tubing holds recirculating hot water for the space heating needs, which heats objects to 86°. Since the object of radiant heat is to create a temperature that is higher than the human surface skin temperature of 81ü to maintain a comfortable level, a temperature of 86ü would provide a “warm enough” atmosphere.

The water heater by itself would generate water heat and domestic potable water. This would be effective to heat radiant panels. Carpenter said that the contractors would need to know how to pipe and install the specific design.

Publication date: 05/07/2001