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2.5" thick wood floors over radiant plates/tubes

J_man Member Posts: 8
Got a client needing warm floors for a nerve condition. 1300 sf in Portland Oregon. 1962 house, nicely built. Floor is framed 4' o.c. with 4"x8" beams. Subfloor is 2" t&g. Finish floor is 7/16" x3" red oak.

I'm proposing Vitoden 200 19kw on continuous circ off outdoor reset with plates/tubes 8"o.c. Trying to run as low a temp continously as possible. This unit modulates down to 12kbtu - sweet! We'll insulate under with r25 batts tight against tubes. There are no systems like this out here (I moved from CO). I've never run through this thick of wood before. We don't have huge heat load here, but when it gets cold folks freak out. We will be adding attic insulation to r50, too.

Any experience, guidance or suggestions very much appreciated. I will have to make sure this can work, as my warranty supports absolute satisfaction.


an old wet head


  • Tinman
    Tinman Member Posts: 2,804
    edited May 2014
    I did

    a job very similar to this 8 years ago. Huge house in the suburbs of Chicago. 2 sheets of 3/4" CDX plywood beneath hardwood throughout. Heavy aluminum extruded plates beneath floor the subfloor with 1/2" tubing and well insulated beneath the plates. My supply water temps are in the ballpark of 118 degrees. 2 x 6 construction, very well insulated. They've never had an issue heating the house. I used Uponor's Advanced Design Suite software in my design. I made sure the numbers being input were right and then I just trusted the math. I was just there last week to service their 3 Space Pak systems. All is well.
    Steve Minnich
  • hot_rod
    hot_rod Member Posts: 19,273
    Do a load calc

    And determine EXACTLY how much the floor needs to provide to cover the load. Then determine the supply temperature required. With that much wood to drive the energy through you may not be able to cover the loads at design conditions without excessively high supply

    A radiant design program will do all these calcs such as required load, tube spacing flow rates, etc. it will also alert you if supplemental heat is needed.

    Don't guess on a thick build up like that.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • J_man
    J_man Member Posts: 8
    Heat calcs

    Have been done. Twice by different techs. 23kbtu/hr.

    There is also backup ducted heat pump system.

    I'll try to track down a radiant design program to confirm supply temps. But do you feel this is tenable as designed? Alternate design strategies?

  • RobG
    RobG Member Posts: 1,850
    Lots of wood

    That's allot of wood to heat through. I would use Uponor ADS software to run the numbers. The problem I think you will run into is the fact that the customer needs warm floors. IF you can heat through the flooring you run the risk of over heating the space (and damaging the flooring). Most of the time the floor may be neutral, maybe cool, not warm. I would be wary of getting myself into a situation where warm floors and a cool space were necessary. The customer may have to run the AC and the heat to maintain a comfortable environment.

    Tough Situation


  • hot_rod
    hot_rod Member Posts: 19,273
    BTU/sq. ft

    is the number you want to know. It will vary from room to room. Floor output "rule of thumb" is 2 btu output per every degree difference between ambient air temperature and floor surface.

    So a 68F room temperature with an 82F floor surface would give you @ 28 btu/ sq. ft output.

    Then you need to calculate what supply temperature would be required to get that surface temperature. That 2.5 build up would be around an R-3 according to the RPA RadPad.

    Using the RadPad simulator you need around 150F supply temperature. You want that surface temperature as even as possible across the floor to get the required output. Good transfer plates 8" on center may get you there.

    25-27 btu/ square foot is about the best you can expect from a wood floor, without getting un-comfortably warm surface temperatures. Excessive supply temperatures below that could cause harm to the wood sub and finish floor.

    Some installers limit the supply temperature to 140F when dealing with wood floors With subfloors that have glues, like plywoods and press type subflooring, go with the manufacturers suggested temperature max.

    You want to keep an eye on humidity levels when you run hot systems, also. Drying the wood may cause shrinkage and panelization where large sections shrink and open large cracks between the flooring boards. If you are in a dry climate a humidifier may be worth looking into.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jackline
    jackline Member Posts: 1
    Harwood Floors

    You can also use hardwood floors for a warm flooring effect, and it is also known for its durability and low maintenance cost.