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Adding a radiant manifold to existing single zone loop

chippy2
chippy2 Member Posts: 4
in Radiant Heating

ok just trying to think this through ahead of time. I have read books and articles on this but theory and practice are not the same

Existing system is 1 zone fin tube with condensing boiler see pics attached

I already had to remove half the old loop for renovation reasons and would like to add a 4 zone manifold with underfloor PEX

Trying to understand the controls for the circulators and thermostats.

Questions:

  1. does primary loop need to be a specific length vs the circ pump
  2. In my “to be” pic does C3 need to run continuously?
  3. How to determine pump size for each circuit?
IMG_4295.jpeg IMG_4296.jpeg

all feedback appreciated

Comments

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,552
    edited September 24

    What kind of boiler do you have? Atmospheric? Condensing?

    If your house is under 4,000 square feet, a Taco 007 or Grundfos 15-42 should work.

    0-10.jpg
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • chippy2
    chippy2 Member Posts: 4
    image.jpeg

    condensing boiler

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 11,091
    edited September 24

    Not a condensing boiler.

    Look at the vent pipe. A condensing boiler would use a plastic vent pipe because all the flue gas condensation would rot the galvanized vent connector away in a year. According to the manual this is a better way to do the near boiler piping if you want less problems with air in the system.

    Screenshot 2025-09-24 at 6.13.08 PM.png

    Assuming that you are connecting to standard Baseboard heating units with 3/4" copper tube. The circulator on the return indicates the installer didn't read the manual and followed the directions his father who taught him to do it that way.

    Edward Young Retired

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

    Alan (California Radiant) Forbes
  • hot_rod
    hot_rod Member Posts: 25,672

    here are a couple ideas and a link to an article explaining them.

    IMG_1084.png

    https://www.pmmag.com/articles/84495-a-little-floor-warming-please-john-siegenthaler

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 11,091
    edited September 24

    Now adding a radiant floor zone to your existing system will require draining water from the boiler (so you may want to upgrade your near boiler piping at this time) and connecting the zone this way. This is the bare minimum that will work.

    Screenshot 2025-09-24 at 6.13.08 PM.jpg A.jpg

    The controls will need to be added so when thermostat that operated C2 calls for heat , C1 will not operate but the burner will operate. depending on what is currently controlling the boiler, that can be done with a ZC or ZR terminal and a Taco SR501 or equal. Or a Taco SR 503 or equal.

    I can draw you the wiring diagram if you want me to.

    Edward Young Retired

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

  • chippy2
    chippy2 Member Posts: 4

    ed. Thanks for this info. A wiring diagram would definitely help me Thanks

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 11,091
    Screenshot 2025-09-28 at 11.11.24 AM.png

    Any Questions?

    Edward Young Retired

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

    Alan (California Radiant) Forbes

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