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What’s the best depth (from the upper surface) for PEX tubing in concrete slab?

cabinflyer | Posted in General Questions on

Getting ready to do a walkout basement build in far Northern Minnesota. 1140 sq. ft. ICF R-37 walls. I’m going to put put somewhere between 4-6″ of foam over crushed surface, vapor barrier, then concrete. Some have posted about a crete-heat type but others have said to raise the PEX into the slab. The concrete guy says he’s OK with chairs.

Is there a overall preference out there?

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  1. SwitchgrassFarmer | | #1

    Google: "John Siegenthaler Tubing Depth" and you will find more than you will ever want to know about this. For example see this article:

    I suspect John would also ask you what your heat source was. In our case, with a geothermal water-water system, he was very concerned about our ability to make hot enough water. As such he strongly suggested that we pull our PEX-AL to the top of the slab as we poured the concrete. Now it was a struggle to make that happen; just keeping the concrete guys from kneeling a wheelbarrow onto the PEX was a battle. On the last pour one of the GC's crew members actually followed along and did an assist by pulling up the PEX.

  2. user-2890856 | | #2

    Mid depth of the slab or at the elevation of the top of the chairs is sufficient . Any higher than that you run the very real risk of the tubing being damaged if control joints are to be cut . If control joints will be included as a detail of the slab such as is sometimes the case make sure to bring the tubing out of the bottom of the slab leaving a belly in the tubing directly below the control joint . The tubing will have the room it needs to move in this way . Fasten the tubing often so it does not rise up too high in the slab to avoid saw cutting damage if joints are to be cut .

    Water temp is a concern but considering you have an R37 ICF wall system and your Northern Minnesota location I would suspect that temps above 120* @ design load would be conservative . Room by room heat loads should certainly be done to insure you zone the slab properly to avoid SHG issues and other things that can make a radiant slab home or any home for that matter uncomfortable .

    Request that the concrete be installed without the use of wheel barrows and the like to avoid tubing damage also .

    The following was posted by R Value Homes in Michigan . Myself and David Butler designed the HVAC in this home . It is radiant , R23 ICF in Michigan . Garage is also heated and entire heated area is right around 4,000 sf . Highest SWT for this home is 120* at -15 .

    This is a remarkable summary of energy bills from an ICF home we built with a 2 stall ICF garage. HVAC is engineered; radiant heat with natural gas boiler. The home is 3600 sq.ft., not including the garage.

  3. Jon_R | | #3

    For anyone concerned about "best" slab or radiator efficiency, be sure to look at the dollar/year difference (vs % efficiency). For example, how much effort or risk is $20/year worth?

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