I have an indirect hot water heater HTP/Superstor SUU-119 and the heating loop looks like this:

enter image description here

I am wondering whether this is correct because it seems weird to me that what appears to be the supply (hot) side of the boiler is going into the middle of the tank. Since the cold water is delivered to the bottom of the tank, I thought the supply from the boiler would go into the bottom.

  • probably less work for the circulator pump this way ...... the hot water cools and starts to sink to the bottom of the heat exchanger because of increased density ...... the water would probably circulate even if the pump stopped ...... you also get hot water at the top of the tank slightly sooner than if the heat exchanger circulated in the opposite direction
    – jsotola
    Mar 2, 2019 at 4:48

1 Answer 1


Yes it's a fairly common setup. As the heated water enters it rises in the tank. The return to the boiler is still quite hot and transfers heat to the cold domestic entering the tank. If the hot from the boiler enters the bottom the heated domestic ends up close to the same temperature as the boiler return and thus is unable to transfer heat. The setup in your picture is called counterflow heat exchange and it is typically the more efficient method. The other method is called parallel heat exchange if you are interested in investigating further.

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