New safety rules issued by the American National Standard Institute say a water heater intended for use on a hybrid system must now carry the warning that it cannot be connected into an existing heating system previously containing non-potable water.
This is to prevent possible contamination of the potable water used for cooking and washing, since the hybrid system attempts to use the same potable water for circulation through the space-heating system.
The Better Heating-Cooling Council says this cross-connection between the two different types of systems could create problems if the water in the space-heating contains non-potable chemicals.
The homeowner may not be aware that chemicals previously were introduced into the sealed space-heating system. Water heaters which are not designed and manufactured for use in hybrid systems must be clearly marked so they can be used only for heating potable water. The council says it fears homeowners may not realize the permanent hot water in a sealed hydronic system is not the same as the flow of fresh water through a domestic water heater.