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radiant heat: Concrete slab in middle of kitchen, unheated perimeter slab, expansion joint advice

Hi I want to install tiles over radiant heat in my kitchen that has a concrete slab. I think i will go with the bekotec foam panels as the overall height is max 1 3/4 inches thick including concrete. Head room is also a factor. Thing is, its a kitchen with cabinets and I don't want to heat the cabinets, I want to use the panels in just the middle of the room. So there would be a 1 3/4 radiant slab in the middle and a 1 3/4 solid unheated perimeter slab. But this leads to the question about thermal expansion. If the radiant slab expands it will compress against the unheated perimeter slab. Whats the best way to handle this?

Hide the expansion gap under the kitchen cabinets? Not quite sure how to handle the gap under the fridge though.

Cant find anything on this perhaps I'm missing an important search term. Can someone point me in the right direction?



  • Jamie Hall
    Jamie Hall Member Posts: 21,541
    Since the radiant floor will never actually get that hot (you hope -- 90 F is about the hottest you'd ever want it) the expansion won't be that much -- though you'll have to take it into account. I would expect that their Movement Joint Profile -- Schluter®-DILEX-DFP -- would be appropriate to use at the perimeter of the heated area. I would place it at the front of the cabinets, and I would continue it right straight across in front of the refrigerator.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nibs
    nibs Member Posts: 499
    Two suggestions, add fiber to the cement mix, it really reduces cracking, I prefer the soft fiber type, as you never know it is there until you try to break the concrete.
    Second, if your boiler will permit set it to increase the supply water temperature slowly, our Rinnai allows an increase of 1 degree F per minute so the concrete warms more evenly. Have no empirical evidence for this, but experience tells me it is a good idea.
  • Gordy
    Gordy Member Posts: 9,537
    edited February 2020
    The slab will be one unit. Use crack isolation membrane for tile installation.

    i wouldn’t bother with control joints unless the kitchen is huge.

    Word of advice, extend the radiant tubing so it is at the toe kick area of the cabinets. When you stand at the counter that’s where your feet will be.
  • mattmia2
    mattmia2 Member Posts: 8,434
    I'd be more concerned about having enough exposed floor area to get the heat output you need.
  • Gordy
    Gordy Member Posts: 9,537
    Kitchens do present a challenge for floor area depending on the load requirement.

    Ceiling radiant is an option to supplement the floor, or panel rads sized for lower operating temps. If there is an area for one.