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Do I need a mixing valve?

WillTheGreat Member Posts: 6
edited January 2019 in Radiant Heating
This might seem like a very dumb question, but I'm curious if I need a mixing valve for my planned set up.

I want to run my entire system on 1 pump (grundfos up26-99). I have 2 zones (upstairs and downstairs) with 8 loops per zone (1/2" pex 240-260 ft per loop). 1 zone would be placed about 30' of 1" pex away from the boiler room. I need about .5ish gpm per loop, and I'd like to keep the entire system 1".

I'm using a Navien NCB240, the house is in northern CA so the system is primarily used to maintain temperature, house is 3500 sq ft of 2x6 construction, R23 walls w/ 2" of closed cell and R38 in the rafter. Anyways it seems like I can adjust the temperature and cap the boiler water under 105 degrees or even use their outdoor sensor which has a setting that keeps the boiler water between 80-105 when in use. Or even cap it at 95 degrees in my case.

What I'm seeing is a mixing valve only creates major restrictions to my system. The Taco 5004 I have shows like a 20psi pressure drop at 12-14 gpm... That pretty much renders my oversized pump useless unless I up size the mixing valve to like 1.5" or splurge on a high flow one. Radiant is my only loop in the system, would it be reasonable to just remove the mixing valve and just tee my return to the supply?


  • SuperTech
    SuperTech Member Posts: 1,792
    You should get the Taco I series mixing valve. That will solve all your problems if installed correctly.
  • Rich_49
    Rich_49 Member Posts: 2,692
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Zman
    Zman Member Posts: 7,330
    You are doing a one temp system with a condensing boiler, correct?
    For this you would not need a mixing valve. Just install the outdoor sensor and do outdoor reset.

    For the pump, I believe boiler has one on board and is designed for primary/secondary.
    For the radiant side, the 26-99 would not be a bad choice on speed one. As long as you don't have much restriction in the manifolds and plumbing, you could probably run a grundfos alpha which is a little less expensive and much more efficient. We would need little more info to help with that one.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • WillTheGreat
    WillTheGreat Member Posts: 6
    edited January 2019
    Thanks Zman, that's exactly what I'm doing. One temp with a condensing boiler. I ordered most of the material already, so it's reassuring to know I can save a few bucks and some parts.