An open radiant system is where radiant floor heat is mixed with domestic hot water. This condition, may create a hazardous situation, because the low water temperature (below 140 degrees) is conducive to bacteria growth in the tubing. It is best to keep the domestic water system separated from the heating system water. For information on safe potable hot water go to the Centers for Disease Control website at www.cdc.gov.
Play it safe. Keep the two systems separate.
It is best to use the closed system concept when designing a radiant heating system. Aside from the bacteria potential, the closed system just works better. Closed system components are less expensive because an open system requires bronze or stainless steel pumps and fittings instead of cast iron. In an open system, oxygen is constantly being introduced into the system with incoming water, while in a closed system the original fill water, once vented of air, remains in the system for the life of the system.
WE DO NOT RECOMMEND OR SUPPORT OPEN-LOOP HEATING SYSTEMS
The temperature requirements for healthy domestic hot water and the low temperature needs of your radiant floor are very different. This opinion is based upon our experience along with the national, state and university studies and warnings.
The federal Centers for Disease Control websites (www.cdc.gov) say that 8,000 to 18,000 people contract Legionnaires' disease each year, with the illness fatal in 5%-30% of the cases.
The CDC study recaps data documenting the presence of Legionella bacteria in residential water systems because of the water heaters being set below 140 degrees Fahrenheit in order to prevent scalding injuries. It's a perfect habitat for growth. Because the bacterium enjoys warm water environments, it's a potential problem in hot water distribution systems.
We would be happy to help you with a closed system using a boiler designed specifically for radiant floor heat
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