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Why we do not Recommend open-loop heating systems

What is an Open Loop Heating System? It is any system where you mix heating water and drinking hot water (potable) in the same system.

The low temperatures of a radiant floor system can become a breeding ground for potentially fatal bacteria. This opinion is based upon our experience along with National, state and university studies and warnings. This is what some sources say about safe potable water temperatures.

Contracting potentially fatal, pneumonia-like Legionnaires' disease from hot water that isn't hot enough. Research, published a few years ago (see website makes clear the dangers of Legionella bacteria and how grossly under diagnosed Legionnaires' disease is. (Legionella is a water-borne bacterium and is the cause of Legionnaires disease) The title of the published study is Legionnaires' Disease Contracted from Patient Homes: The Coming of the Third Plague?

Indeed, the federal Centers for Disease Control website ( says that 8,000 to 18,000 people contract Legionnaires' disease each year, with the illness fatal in 5%-30% of the cases. The study recaps data documenting the presence of Legionella bacteria in residential water systems because of water heaters being set above 95°F and below 140°F is a perfect habitat for growth. Because the bacterium enjoys warm water environments, it's a potential problem in hot water distribution systems.

When your domestic hot water tank reach temperatures above 120°F, it is important to put in an anti scalding mixing valve to prevent scalding injuries.

If you have an open loop heating system tied into you hot water or cold water domestic water system - there are ways to separate the two with the use of a Flat Plate Heat Exchanger and an additional pump or two. Contact us about this if you want more info.