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Strategy for Minimizing Floor Height Using Radiant Heat Floor Piping

user-2876363 | Posted in Green Building Techniques on

Hello all, I am planning to lay pex pipe for radiant hydronic heating in my basement lower level. Currently there is a 4 inch slab with a vapor barrier under that. I want to minimize raising the floor since it is a remodel but I realize I will be raising up door thresholds and reframing stairs. I am planning to glue down 1 inch of R-5 rigid foam, then glue 5/8 inch plywood sleepers directly to the foam and setting 3/8 pex A tubes into heat transfer plates between the sleepers. Then an engineered wood floor that is 1/2 inch thick on top of the heat plates and tubes and sleepers. I am wondering if this is a fairly acceptable approach? Since I wish to increase floor height as little as possible, I’m hoping that sleepers placed directly on foam will be rigid enough if i use adhesive all around?

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Replies

  1. Expert Member
    NICK KEENAN | | #1

    Sounds OK to me.

    Unless you've done every possible calculation and it checks out on all of them, I'd give up the 1/8" and go with 1/2" tubing instead of 3/8". The difference in flow is substantial. The #1 problem people have with radiant floors is undersizing them and being unable to upsize once they're installed.

    1. Expert Member
      AKOS TOTH | | #2

      I would disagree. The number one problem with radiant floors is not doing the design upfront.

      You can use any size pipe as long as things are sized properly. I've used 5/16" PEX without issues, works fantastic and takes up only 1/2" of height.

      The better question is what is the heat load in the basement, what is the sqft of the place and what is your hot water heat source?

      A typical insulated basement needs very little heat (think in the neighborhood of 5000 to 7000 BTU), this generally means you don't need to heat the entire surface. You can much better comfort for way less money by only heating the high traffic areas. DIYing your own floor heat panels is a lot of extra work, the commercial systems are expensive, but not much more than all the monkeying you'll have to do get this right. Bonus is they come with specs and design manual to help you get the most out of the system.

      In a typical basement with 50F ground, 70F room and say 80F floor temperature per 400sqft of heated area
      -with R5 insulation you are delivering 8000BTU to the room and loosing 2400BTU to the soil, so 30% of your heat output. Not great.
      -with R10 that drops to 15%, better but still not that good.

      You really want at least 2", 3" is better. I have done 1" when tight on height but only for a small area such as a bathroom.

      1. Expert Member
        NICK KEENAN | | #3

        You're right, of course. Design it right. But if you're going to design it wrong, err on the side of oversizing the emitters!

      2. Expert Member
        NICK KEENAN | | #6

        >In a typical basement with 50F ground, 70F room and say 80F floor temperature per 400sqft of heated area
        -with R5 insulation you are delivering 8000BTU to the room and loosing 2400BTU to the soil, so 30% of your heat output. Not great.
        -with R10 that drops to 15%, better but still not that good.

        I would argue that with an interior temperature of 70F and the R5 floor, heat loss through the floor is going to be 1600 BTU anyway, so it's only an extra 800 BTU that you lose by having the 80F surface next to the floor. So that's 10%. Going to R10 for the floor has more of an impact on the overall heat loss than on the heat loss specific to the radiant floor.

        Yes, it would be more efficient to have the heating on an interior surface, such as the ceiling. But at the end of the day heat is about comfort not efficiency.

  2. charlie_sullivan | | #4

    Have you considered radiant ceiling panels? You'll potentially lose less height, and you'll lose less heat into the ground than you do with only R5, and maybe you can add a little more insulation.

    What R5 insulation are you using? If XPS, are you aware of the huge climate impact that most XPS has? Alternative with much lower climate impact include graphite-infused EPS ("GPS") and the new Owens Corning NGX foam, which you supposedly can now order.

  3. jberks | | #5

    I think this is a good application for warmboard or quicktrack. You'll get a much more solid floor feeling on the feet and less monkeying around than with strips of plywood as sleepers.

    Something to consider , But it does have its associated cost, so it's a matter of your approach.

    Jamie

    1. Expert Member
      Dana Dorsett | | #7

      >"I think this is a good application for warmboard or quicktrack. You'll get a much more solid floor feeling on the feet and less monkeying around than with strips of plywood as sleepers."

      +1 !!!

      Sleepers don't buy you anything here. A panelized system is going to be easier to specify and install. There are others.

      For basement slab retrofits Roth Panels are a decent low height option to consider too.
      Roth Panels are aluminum clad one-side EPS with snap-in channels designed for PEX, and can be glued to the slab, with a half-inch plywood subfloor above. I believe the panels designed for 3/8" pex are 3/8" thick. If the slab is dead-flat the plywood can be glued to the Roth Panels, but it's probably better to throw in a few TapCons per sheet to avoid "potato chipping" or waves forming from seasonal humidity changes in the plywood.

      http://www.roth-usa.com/products_radiant_panelsystem.cfm

      At the very low heat loads of basements, with the aluminum cladding heat spreader on top of the panels the water temp requirements stay very low, and the losses to the slab aren't terrible even though the EPS is only 3/8" thick in the bottoms of the channels. It's fine to install it over a layer of foam board if a higher R is warranted.

      1. Expert Member
        NICK KEENAN | | #8

        Hey Dana --

        Can the Roth Panels be installed without the plywood subfloor with a floating floor? That would help with both the height and also with the efficiency. Or is it too rickety?

        1. Expert Member
          Dana Dorsett | | #11

          I'm not really sure what you can get away with on top of slab-supported Roth- it may depend on just how rigid the floating floor is. Being fully supported by a slab the EPS isn't very compressible, and the integrated #24 gauge aluminum heat spreader/facer stiffens it up a LOT. The main issues would be what happens with the flooring along the seams of adjacent Roth panels. When in doubt consult the manufacturer.

  4. user-2876363 | | #9

    Thank you all for comments, I have more things to consider and think about! Generally all the panel systems seem so expensive i was hoping to avoid them, otherwise I am sure they are good products.

  5. thegiz | | #10

    What climate zone are you in? Maybe I missed that but you may be better off just insulating the floor for warmth if you are worried about cost and ceiling height depending on where you are. I'm in NY and my cousin who installed radiant floor heat told me it ended up costing him a fortune to run. Now I'm far from expert but what you have on your walls will play a huge part as well.

    1. Expert Member
      AKOS TOTH | | #12

      You are almost always better off to insulate a basement. A well sealed and insulated basement is surprisingly comfortable without any fancy heat, sometimes you can even overheat the basement if you have a lot of uninsulated ducting or hydronic piping in the celling.

      I would bet the floor heat that was a fortune to run was done without an insulated slab. Without any R value bellow the heated slab, you are mostly heating the earth not the room. Dirt is an excellent conductor of heat so you need to put a LOT of heat into it before any heat makes it into the basement, thus the silly energy bill.

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