DHW zone piped before expansion tank- is this a problem?

Ben Thorp

Hello: I am a homeowner who recently purchased a foreclosed 3-family tenament house. The existing heat system had been installed so that the supply line branched to an indirect HW tank, then continued to the incoming water line with air scoop & expansion tank, then to the 3 heating zones. All four zones have Taco 007 circulator pumps with flo-check valves. My heat guy says the setup should be re-piped so that the HW zone comes after the air scoop & expansion tank to avoid negative pressure problems, but as I was cleaning up the basement, I came across a copy of a diagram from "Residential Hydronic Heating (The I=B=R Coursebook)", specifically diagram 6-24, which seemed to justify the existing set-up. I went back to my heat guy with this diagram, and he wasn't sure whether it would work alright, because of the complexity of having one pump running before the air scoop/ expansion tank, and three additional ones running after it. He suggested I post the question here: does anyone have any thoughts?

martin

DHW Piping

The piping systtem will work perfectlly fine. Its usually done like that to stop thermal creep in the summer when the rest of the zones are down.

Ben Thorp

DHW piping

Thank you very much for the reply. The only aspect of my setup that differs from the diagram in the book is that the diagram has a flo-check on BOTH the supply and return ends of the heating loops, whereas my system only has flo-checks on the supply sides. I'm assuming the second set of flo-checks has something to do with preventing 'thermal creep' as well- should I have my heat guy put them on, or just leave it as it stands?

martin

Thermal Creep

You will probably get some thermal creep on the return side, my advice wait and see.