Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Mixing Valve Question

Options
smithsfan
smithsfan Member Posts: 13
So I'm doing a boiler install. I've got a mixing valve for the radiant infloor heat. I know usually you tie in the cold water side of the mixing valve into the return pipe of the radiant loop. Instead, is it a big deal if I tie it in to the return piping on the primary loop itself? It shouldn't matter correct?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,554
    Options
    The primary loop will probably be hotter than the return from the radiant piping, since it is also getting flow directly from the boiler. If -- and only if -- you tied in beyond the last return would it work reasonably well. Otherwise it is entirely possible that the primary loop would be at least as hot as your desired output!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • smithsfan
    smithsfan Member Posts: 13
    Options

    The primary loop will probably be hotter than the return from the radiant piping, since it is also getting flow directly from the boiler. If -- and only if -- you tied in beyond the last return would it work reasonably well. Otherwise it is entirely possible that the primary loop would be at least as hot as your desired output!

    Good points, I was thinking the same thing, having it last on the primary if I go that route. It does seem best practice is to tie it into the return on the radiant loop itself.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,157
    edited July 2022
    Options
    Here is a diagram that comes to mind with your original query:
    this one will work:


    This one will not work:


    Seeing it like this will help make sense of the fact that the return water to the boiler may be too hot to get the needed low temperature water to the cold side of the mix valve as @Jamie Hall stated

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • smithsfan
    smithsfan Member Posts: 13
    Options

    Here is a diagram that comes to mind with your original query:
    this one will work:


    This one will not work:


    Seeing it like this will help make sense of the fact that the return water to the boiler may be too hot to get the needed low temperature water to the cold side of the mix valve as @Jamie Hall stated

    Thanks, I wonder if I should put the isolation drain for purging before or after where the mixing valve cold supply tees into the radiant return?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,157
    edited July 2022
    Options
    smithsfan said:

    Thanks, I wonder if I should put the isolation drain for purging before or after where the mixing valve cold supply tees into the radiant return?

    Not sure of exactly your query is asking. Are you asking about purging air from the radiant loops in order to commission the radiant floor loops? I would think the purge valves and isolation valves were built into the manifolds. As a professional I always used the manufacturers manifold kits. they came with everything needed. If you are building your own manifold and purge system from scratch, you would get a picture of a "ready made" manifold and purge setup and copy that. Seems like a lot of work to reinvent the (Wheel) stuff others have already made easy for you.

    Can you draw a diagram for clarity? As you can tell... I Like To See A Picture!

    Edit: look at this video https://www.youtube.com/watch?v=5xrl_1k5YvY from supplyhouse.com

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,157
    edited July 2022
    Options
    Depending on your design this is how I might set up the purge valves and isolation valves.
    The blue dash line is the water pressure from the fill valve of the entire system providing pressure to the loops. The individual loop isolation valves are all closed except for the loop that is being purged. the isolation valve after the purge valve is closed so all the purge air and water must come from the loop. As long as the water entering the "HOT" port of the mix valve is cool, that valve port will be open full to the "MIX" port for purging

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • hot_rod
    hot_rod Member Posts: 22,382
    edited July 2022
    Options
    you need need the cooler water returning from the radiant to mix down the hot from the primary. A mix valve can only regulate with a hot and a cold or cooler flow.  Needs to be about 20 degrees difference between mix out and ghost in to work. A Webstone purge ball valve simplifies purging
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    smithsfan
  • heatdoc1
    heatdoc1 Member Posts: 14
    Options
    Ed I know its off topic but what program are using for these piping diagrams?
    John Ringel
    Senior Technical Support Specialist
    Energy Kinetics
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,157
    Options
    heatdoc1 said:

    Ed I know its off topic but what program are using for these piping diagrams?

    I am using Paint S on a MacBook. Windows has Paintbrush. It is time consuming but I can copy and past a screenshot to Paint S and use the drawing tools to place lines circles, other shapes and text where ever I want. one pixel at a time if i'm inclined.

    This is how I take the existing drawing pr photo that you are already familiar with, and doctor it up with my idea and explanation. Easier to follow a small change to something you already understand.

    Mr.Ed

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    heatdoc1