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radiant tubes in a concrete slab-dumb question

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by captaintone, Feb 21, 2009.

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  1. barnartist

    barnartist Minister of Fire

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    Heaterman, a few years ago, my cousin did the same thing. Used some kind of black roll material, it had 2 layers of bubble and maybe a thin layer of foam. My cousin can't keep enough wood. He abandoned a gasifier for a CB. Now we are looking for other options. I love my radiant heat in my house. I still feel bad for those who messed up, because now it can't be fixed.

    It would be fun to talk to the John Deere owner in a year or 2, see how they are doing.

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  2. sdrobertson

    sdrobertson Minister of Fire

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    Probably cheapest way to fix this problem would be to find a junk furnace and hook it up to a water to air heat exchanger. He could even run a little duct work to heat the whole building. Not ideal, but cheap and he could use filters to clean the air also. I vote for a new federal "radiant heating czar" with allot of important regulations of maybe some education for installers.
  3. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Could we just have subsidized clue-by-fours, instead? :)

    Joe
  4. AOTO

    AOTO New Member

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    It is attached via these little black clips that look like the opposite of a fish hook. It was done by this stapler looking thing that had the black staples push down on the tubing and as it goes into the blue board, it hooks on the out side of the clip. I'll get my camera and take a picture of it. I saved a piece of the insulation set-up that shows everything. My barn also has no problem staying above 50, even when it's 9 F outside.

    Attached Files:

  5. GKG-MO

    GKG-MO New Member

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    I'm not personally a fan of those plastic U hooks. Once the floor is poured their fine but they tend to pull out during the pour and then the tubing likes to float to the top of your concrete. NOT GOOD. Especially if your saw cutting your expansion joints. Either lay down 6" wire mesh and zip tie the pex to that or they make a clip the screws in similarly to a wall anchor that the pex clips into. They take a little longer to install than the U hooks but easy in, easy out.

    As others have said use plenty of insulation. The more you spend now the more you save later. Hot air rises. Radiant heat radiates through the easiest path, witch could be into the ground if your not careful.
  6. captaintone

    captaintone New Member

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    Great set up. How long does it take for you shop to warm up? I only ask because I aslo want to heat a detached garage. Its not a place I will be all the time and worry that it will take to long to warm. Meaning I might be done working in there before the garage warms up.
  7. Der Fuirmeister

    Der Fuirmeister Member

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    Use glycol. Same for any slab that might freeze.
  8. Der Fuirmeister

    Der Fuirmeister Member

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    Radiant doesn't react quickly to demand changes like forced air does. If you need quick / short term temp changes you might consider an added source like a cheap furnace or unit heater to bring up to temp.
  9. captaintone

    captaintone New Member

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    Thats what I thought. I didnt think radiant would heat up fast enough if I am not using the garage all day every day. I am going to look into an alternative for the garage.
  10. Der Fuirmeister

    Der Fuirmeister Member

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    Heaterman, What do you recommend to prevent concrete floors from cracking when using foam?

    Was the 1-1/2 inch foam what you normally would use?
  11. deerefanatic

    deerefanatic Minister of Fire

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    I and my neighbor were talking on that this last summer. We came to the conclusion that if we EVER pour concrete for ANYTHING that will be inside, we're gonna lay pex in it; just for the simple reason of the pex is a small percentage of the cost of the concrete, and it's not something you can do later.... Even if it doesn't get used for 10 years, it's there if I want it in the future.... Just my $.02
  12. Der Fuirmeister

    Der Fuirmeister Member

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  13. Chris S

    Chris S New Member

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    re: will cracks affect tubing?

    For anyone that has not seen a pex demo.... I was at the Uponor booth at a recent trade show. They took a piece of 1/2 pex approx 5" long, and put it inti a machine that stretched it to approximately twice it length, without failure. The center was down to about 1/4" at that point. They then took a heat gun a it returned back to it's original shape, which not all pex will do but...
    The point is that the little bit of stretch you will experience in a shrinkage crack is truly insignificant to the tubing.
    A displaced crack, one that you could trip on is more of a concern. A small shifting will not break or shear the tubing, but could pinch it if the crack were significant.
    As pointed out by many, a stable base is the best beginning- well compacted etc.
  14. heaterman

    heaterman Minister of Fire

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    Best antidote for cracking is a good concrete man, slow set up on the crete and a solid and even grade to pour on. The foam and tube really have little to do with it.

    We use 1.5" foam for 4" pours and 2" for 6" thick floors. Some will say it's a waste but we do the whole floor with the same stuff.

    One thing that you can say is a negative regarding thick slab radiant is response time. You just can't expect that mass of cement to produce heat quickly or to shut down quickly. I have installed what is basically a two stage setup in some places where the owner insisted on turning it down. We usually set up the floor to run at a low temp that will maintain 45-55* and then install some other type of emitter, radiators, baseboard, fan coils to pick up the room temp from the setback point. Best to just minimize the heat loss and let it run.

    Response time for a poorly insulated slab can be measured in days, even weeks, not hours.
  15. Greenfield Dave

    Greenfield Dave Member

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    Hi Guys! Long time lurker, first time poster. Here's my situation.

    I built a 36X48 garage with loft, and used knowledge from this site and others to put PEX in the floor. 1500' to be exact, in 5 zones. Put 2"pink board down, used the twist in PEX clamps, thought is was Miller time! But I didn't put clamps at the point of the loops, and they floated up in the concrete mix. Woops! So we decided not to make saw cuts, it didn't crack too bad, it does have fiber in it. I have insulated all the 2X6 walls and put OSB on them, but the ceiling will have to wait till money is in season! I just bought a stainless manifold, and am going to heat the system primarily with my OWB, but will use an electric water heater for backup/supplemental heat. I have a sidearm heat exchanger, expansion tank, and just enough skills to be dangerous!

    My questions for you experts are:
    1. How big of a pump do I use?
    2. Should I control the incoming temperature to the water heater/sidearm with a tempering valve? Or run that loop wide open and control the temperature to the floor?


    I have a layout of how I think it should be plumbed, but it's too big to attach here.



    Wood Doctor 8000
    Stihl 041 Farm Boss; 009
    POS Swisher log splitter
    House heated with an older boiler, old cast iron radiators and under floor PEX

    Any input is appreciated!!!
    Dave
  16. AOTO

    AOTO New Member

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    I'm running with no heat exchanger and I'm using water. I'm running a Wilo Star 30 to my barn which is 150' from the OWB, then once I get inside, it goes thru a tempering valve and then to a TACO 007. I am running 6 loops, each at approx. 200-250' each. There is also a little trick about looping the lines no greater than 4 1/2 " before the tempering valve. I can tell you that my barn is warm and zero maintenance, however my wood consumption went up 35-40%, but I blame that on using crappy, cheap, insulated Pex underground.

    Attached Files:

  17. Greenfield Dave

    Greenfield Dave Member

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    Nice Job Burning Chunk!!

    I assume the tempering valve was missing from the second picture.. but I understand what you did. I don't understand the 4 1/2" rule you spoke of either, but always obey it.. I need to use the heat exchanger and antifreeze, as I may have the opportunity to go away in the winter! HA! We want to come back to Vermont to celebrate our anniversary this winter, but with the economy, who knows!

    Thanks for the info!!

    Dave
  18. WRVERMONT

    WRVERMONT New Member

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    Heaterman, sounds like those guys should have taken your quote.
    Below are my tips for a good radiant slab.
    1. Good drained foundation of stone.
    2. Insulated with a minumum of 1.5" and better 2" foam board underneath. Insulating the Perimeter is important to.
    3. Moisture barrier (polyethylene)
    4. The use of wire grid reinforcement will make it strong and also help distribute the heat around.
    Below tubing or better yet below and above.
  19. RowCropRenegade

    RowCropRenegade Feeling the Heat

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    This thread seamed to be closest related to what I'm doing.

    I just excavated out the building. Put in 6 inches of stone, except for borders. I bought GreenGuard 2 inch foam insulation for the entire border and floor. The foundation wall is uneven as hell. I'm planning on building out a foam barrier around the jagged areas and filling it with concrete. I don't want a single area of the foundation exposed. I'm anchoring the foam board with masonry screws. Prob 2 per 8 ft.

    After that get the edges filled in with stone, ground perfectly leveled and down with the foam board. 6 mil vapor barrier.

    Comments?
  20. heaterman

    heaterman Minister of Fire

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    Sounds like you are thinking it through nicely. You basically want to have your concrete slab sitting in a foam tub.
  21. RowCropRenegade

    RowCropRenegade Feeling the Heat

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    The vapor barrier above the foam, correct? Then wire mesh.

    They have these stands at lows that hold the wire mesh up 2.5-3". I thought that made alot of sense for what I'm doing. 6 inch pad will have the pex at exactly 3 inches into the pad.

    Comments?
  22. Chris S

    Chris S New Member

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    We generally put the plastic down first, though I don't think it really matters. bar chair, or supports such as you describe don't work especially well with wire- as it's not ridgid.
    What we generally do is lift the wire as the concrete is being placed. This results in the wire being approximately 1/3 of the way into the slab, which is pretty much ideal.
    If the nasons step on it & it's at the bottom, it's not the end of the world.
  23. DaveBP

    DaveBP Minister of Fire

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    I put 8mil poly down on the compacted sand and the foam on top of that. I reasoned the foam can take the beating it will get from the crew but the poly film might not be as durable.
  24. RowCropRenegade

    RowCropRenegade Feeling the Heat

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    do you also put it under the foam on the foundation?
  25. deerefanatic

    deerefanatic Minister of Fire

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    The way our shop was done was a totally different animal......

    According to the previous owners, they ran the bex in a 6" thick bed of sand below the concrete, so if the concrete ever cracked, it wouldn't break the pipes...

    I've never actually been able to heat this shop, but this winter should change that......

    I know I have perimeter insulation, but have no idea what's under the sand bed.....
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