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.

Wood and concrete radiant floor same temp?

grrrdot Member Posts: 10
I have a new-to-me house and I’m finding it has a number of interesting design choices. I had to re-plum the primary/secondary boiler loops to get it flowing correctly and now I’m trying to sort out my second floor radiant heat.

Today the system is configured like this:

Both the first and second floor are using the same circulator and a mixing valve (120F) but each floor is controlled via zone valves.

The first floor is a 650 sqft concrete slab. When the heat is running my IR thermometer says the floor gets up to ~85F at its hottest points. I don’t know how many feet of tubing there are but the floor has alternating cold/hot spots so I’ll guess its not enough or just run weird. I can live with it though because the floor gets the room up to temp.

The second floor is all wood flooring. I’ve poked around and as far as I can tell the whole floor is just wood, no slab. Last night the second floor ran the system for >10 hours but the room did not get above ~65F. ( ~30F outside ) I checked this morning and the return from both second floor circuits are coming back at ~115F. My IR thermometer says the floor itself is only 71-69F. I managed to find a single warm spot at 74F.

We are going to be remodeling house in a year or two so I would like to get this working better without ripping too much apart.
I thought of getting a higher temp mixing valve but not sure what that would do to the concrete floor?
Other idea would be to have the second floor share the full temp water with the radiators? I'm not sure that's safe either.. Any other thoughts?



  • Gordy
    Gordy Member Posts: 9,546
    In reference to the second floor temps, and being wood flooring. Wood flooring manufacturers want 82 max floor temps. However your short fall from that floor temp may be the design of the underfloor radiant detail, in which I assume is unknown, and not accessible to find out. Could be you need to run higher SWT to that zone.

    There are a few different types of radiant floor build details. Each of which require different SWT to the panel.

    Sandwich type above the sub floor with plates which requires lowest SWT
    Sandwich with out plates.
    Staple up Plated under floor
    Staple up No plates under floor.
    Suspended tube under floor.

    Insulation in the joist cavity is crucial to their performance.

    The above types have different SWT requirements for same btu heatload of room. In order from coolest to hottest on my list.

    The concrete floor seems to be fine. The cool spots you pick up are probably between the tube centers.

  • Gordy
    Gordy Member Posts: 9,546
    edited December 2017
    If both floors are using the same mixing valve you may need to add another mixing valve one for each zone so you can use two different SWT.

    cant say I care for the piping schematic.
  • Zman
    Zman Member Posts: 7,547
    I would use 2 different mixing temps. You would eliminate the hot spots and have better comfort if you did outdoor reset rather than fixed temp. The taco I-valves are a simple solution.
    Could you elaborate on the DHW configuration? Is that a reverse indirect tank?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein