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Recommended slab temp under wooden floor?

ba123 Member Posts: 6
Just had a radiant system installed under 3-inch quartersawn oak flooring.  The thermostat allows setting of a maximum slab temperature.  What's the recommended setting for this?

My understanding (as a homeowner not a pro) is that a lower slab temp is better because it will help prevent warping/cupping of the wood floor.  However, a higher slab temp of course heats the room better and is (slightly?) more efficient.  I've read that 85*F is the absolute max slab temp under any kind of wood flooring, but again that lower is better.

Advice appreciated.


  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited December 2010
    Max Surface Temp

    I never want a floor above 80 degree surface temp. Actually haven't come across  many where I would  need anything more than the mid to upper 70's. If my floor surface temp exceeds 80 I add a form of supplemental heat that I can use lower water temperature with such as a panel radiator. 

    Myself nor anyone here can recommend an ideal surface temp. We don't know the heat loss, amount of tubing in the floor and the application. Is the tubing in the slab or is this a joist heating application?' If joist heating did the contractor use heat transfer plates? If so whay type.  Did the contractor who installed the job leave you a copy of the heat loss and radiant design? Did you ask for one?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Andruid_2
    Andruid_2 Member Posts: 42
    radiant slab under wood floor

    "However, a higher slab temp of course heats the room better and is (slightly?) more efficient."

    That really depends on the design data.  If you pump too much heat into a slab (hotter water) then you'll experience overshoot and temperature swings, which is not efficient.  If you pump too little heat into a slab (cooler water) then your equipment will run all day long and not be able to keep up, which is not efficient.  If you have a condensing boiler then cooler water is more efficient.  Regardless of all that, if your installer is savvy, then he did a heat loss and flow analysis and determined the right temperature for the water to be set at.

    As for your wood floor, I would never heat a slab under wood to a surface temperature of more than 85 degrees.  I would be more comfortable with 80 degrees.  And remember that the temperature of the water going out to your floor is going to be higher than your surface temperature, so don't be alarmed if your pipes in the mechanical room get over 100 degrees.
  • ba123
    ba123 Member Posts: 6

    Thanks for the information.  I will call the contractor to get some additional information.  I believe he routed grooves in the plywood subfloor, then put pex in the grooves, and then put the hardwood flooring on top of the subfloor.  He also insulated the bottom of the subfloor (which is over an unheated crawlspace).  But I'm not really sure about all this and will call him to check.
  • Gordan
    Gordan Member Posts: 891
    What do you mean by "slab"?

    The system you're describing would not be considered a radiant slab if there's no concrete slab (or gypsum pour) that's being heated by tubing.
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