Hydronic heating question???

I am an inspector in the Seattle WA area and I have been seeing a lot of Hydronic heating, especially in tall townhomes. They are using the same water heater tank or tankless as the domestic water source. The heating system kicks out great heat and works great. My question?
I though that boilers and/or hydronic heating has to be a closed system, separate from the domestic water source used for showering etc… All of the water heaters being used that I see appear to be just a standard water heater. Maybe I am wrong though.
Is a specific water heater supposed to be used for this to keep a closed system? And if so, how do you tell if it is one?

Thanks everyone,

Tyler Tachell

All the ones I’ve seen are run from a boiler. I have yet to see one run from a water heater. I wouldn’t think a water heater could generate enough sustained heat. I’m curious to see what someone else may think.

Perfectly okay to use WH. Newer versions(in my area) use a separate system for potable water.

Pretty common up here in the Pacific NW with condo conversions and multi-story units. Wait until you start running into the shared TPR / Heater Pressure Relief drain lines. Some AHJ will allow, some won’t.

Been used in our area for a few years no complaints work great … Roy

Tyler please send me your email this one does not work … Thanks Roy


Yes, a specific WH is to be used.

Attached are some pics from a Bradford White WH used for such a system.

There is a heat exchanger inside.

Just like a furnace, but for water instead of air.

Lennox has a setup out there called Complete Heat. Wait until you run into one of these things. I have seen water heaters that had the capability to produce over 300,000 bth/hr, more than enough to heat with. Besides if the hydronic system is a radiant design in the floor or wall the water temperatures are rather low compared to radiators or coils in an air handler.

No longer available … Roy

many law suits .

STOP no longer available Law suits on this unit… Roy