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  • Domestic hot water systems compare very well with other heating systems and National code officials have seen fit to approve them. Radiant heating systems in general have significant health benefits. Low temperatures and low pressures are always good for safety. The “open direct system” is mechanically identical to so called “recirculation” systems which are very common and do not seem to be causing undue problems. Legionella bacteria cannot withstand temperatures above 115° F. You can always reduce the risk of contamination by bacteria by increasing the water temperature, but you will then increase the risk of scalding. It is our opinion that the risk of Legionnaire’s disease in domestic hot water systems is “an emperor with no clothes” that is largely created by special interests groups in the heating industry. Legionnaire’s disease is a reportable disease according to law and public health authorities make every effort to determine the cause when it appears. We are not aware of even a single case of Legionnaire’s disease that was caused by a domestic hot water based heating system. If it were a real issue, there should be many.