05-02 Potable waterline as heat source

Question: 05-02Code Section: 7Date:OBC 2006 Reference:

Question: I’ve inspected an installation using the potable hot water as a heat source.  The cold water passes through a ATakagi T-KD20 instantaneous water heater, to supply the hot water for the radiant heat loop, and has a branch just downstream of the heater to supply potable water to the house.  This branch has a thermostatic mixing valve on it to bring the water down to the code required temperature. The concern I have is that the water in the heating loop will become contaminated, especially over the summer, and that it is not separated from the potable water available to the occupants.

The manufacturer recommends that the recirculating pump run for 60 seconds every 6 hours, and that a priority switch be installed on the cold water inlet to temporarily shut down the pump when water is drawn by the occupant, but is that enough? As an example, the water has been sitting in the heating loop all summer, and has been doing its loops through the heater every 6 hours.  Part way through the cycle the occupant draws off hot water to add to soup.  The water that is present in the heater at that time could have been trapped in the heat loop all summer.  This water would then be supplied to the occupant through the potable water system.

Do you agree with my concern?  Should I request a separate system?

Interpretation: (On. Reg. 403/97) 1. According to the OBC requirement, the proposed installation may render the potable water and becomes non-potable.  Therefore, such a connection is prohibited in accordance with Sentence of the OBC.

2. Authority having jurisdiction can always accept other design or installation methods based on Section 2.7 of the OBC if warranted.  Authority can reject or accept a design proposal if the CSA B214 Standard is being used with a double wall heat exchanger, or by re-circulating water within the heating loop even during summer time and complete with all components/piping which will meet the NSF 61 criteria and potable water piping required by the OBC.