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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Google: "John Siegenthaler Tubing Depth" and you will find more than you will ever want to know about this. For example see this article: http://www.pmengineer.com/articles/92439-exploring-all-the-aspects-of-tubing-depth
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.
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.
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?