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Multi-temp zones without Primary / Secondary?

grrrdotgrrrdot Posts: 10Member
Thanks for any advise on this.
I'm playing around with system ideas to fit in a really tight space. If I can forego a primary/secondary setup it cuts down on the space needed. ( and cost )
I made a sketch of what I'm thinking below. Its supposed to be an HTP UTF boiler w/ outdoor reset running three zones, two zones are panel radiators w/ TRV and one is radiant floor in a concrete slab. On the coldest day the concrete slab needs 125 and around 15 delta T. The panel radiators are 170 and 10 delta T.
From what I read the boiler will shut down if inlet and outlet are more than 55F.

So, would the attached system sketch even work?

My main concern is that in some rare coldest day scenario I could have just the floor calling and it would trigger the 55 deg safety or damage the boiler. But maybe there are other things I missed?


  • ZmanZman Posts: 5,062Member
    I would go primary/secondary. The manufacture requires a min flow of around 1.5 Gpm. The mixing valve could easily turn all the way to cold and starve the boiler of flow.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • grrrdotgrrrdot Posts: 10Member
    Ah, yeah you are right, missed that. Alright then need to figure out P/S.
    HTP cites 6 diameters of straight pipe up and downstream of closely spaced tees. Is that just for the run of the Tees or does that include the branches as well?

  • mattmia2mattmia2 Posts: 121Member
    I don't see why the 55 return would damage the boiler. Am I missing something?
  • Steve MinnichSteve Minnich Posts: 2,467Member
    Its not the water temperature that would damage the boiler, but lack of flow as @Zman said.
    Steve Minnich
    Tell me I can't, and I'll show you I can.
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