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General radiant floor question

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Rick Stanley, Dec 12, 2013.

  1. Rick Stanley

    Rick Stanley Feeling the Heat

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    Hi Everybody,
    My Garn is over a month into its 5th season. I've made improvements on the system each year and it's doing the job quite well these days. Hope everyone is well and your wood sheds are full.
    There is part of an existing building here that has a wood framed floor that has been overlaid with 3-4 in. of concrete. It has a full basement under it and the underside if the wood flooring and joists are easily accessible. I think there are two layers of rough sawn 1" boards and 3-4 inches of concrete. Is it feasible to staple up some tubing and insulate the hell out of it below tubing? Or is that too much mass? I haven't a clue.
    Thank!!
    Rick

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  2. stee6043

    stee6043 Minister of Fire

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    Concrete over wood with a basement underneath? Never heard of such a thing arond these parts. Interesting.

    You'd have quite the uphill battle in getting the slab to change temp. 2" of wood is, in and of itself, quite a barrier. The slab would be great once you got the heat to it. But pushing through 2" of lumber may not be so easy. With proper insulation, maybe not bad? It would surely be slow to respond if you did get it to work.
  3. Rick Stanley

    Rick Stanley Feeling the Heat

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    This place was a commercial egg farm up till the 70's. Certainly not commercial by today's standards, but the space I asked about is a 20 X 40 section of a 40X100 2 story chicken house. This part of the building was used for cleaning, grading, storing and packing eggs for shipment. I have updated part of it for warm weather state approved processing of meat chickens and am thinking about ways to heat it for winter use.
  4. __dan

    __dan Burning Hunk

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    Hey; Just a thought.

    I'm not recommending it because the floor supporting structure has to be rated to carry the added weight, but if the floor joists can take it, you could consider attaching the PEX to the existing concrete surface and pouring a cover layer of 1 1/2 " of added concrete or gypcrete. If the floor can carry the extra weight, that would be sweet.

    It's very possible the PEX embedded concrete surface layer would have a lower material and labor installed cost and the performance would be far superior to staple up under the floor mass, which is an insulator as noted above.

    The concrete embedded surface layer method will have a much wider PEX spacing, maybe 12" compared to 6" or 8" spacing under the floor, and require much lower loop water temp to operate.

    The staple up underside method, the floor is not too much mass. The 2" of wood deck planking is too much insulator.
    BoilerMan and ewdudley like this.
  5. bmblank

    bmblank Minister of Fire

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    I would imagine it would work as long as you don't want any setbacks. Basically one you heat the slab, the slab is what heats the rest of the house. Just expect it to take a day to change the slab temp.
  6. Bob Rohr

    Bob Rohr Minister of Fire

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    Depends on how much heat you are trying to get out of the floor. Do a load calc for the space. If you can, use one of the radiant design programs and it will tell you if the floor alone can carry the heat load, or if supplemental heat will be needed.

    It will give you a number in BTU/ sq. ft. required, and amount of additional heat to be added.

    Uponor, Viega, Watts Radiant are great load programs, designed just for radiant loads.

    Or use a generic load calc, get the BTU number and divide it by the square footage you have available.

    Additional floor covering?

    Two inches of softwood and 4" of concrete is an R 2.6 that will be tough to transfer BTUs through.

    Edge insulation would be a must, at least 2" of foam.

    Radiant ceilings or walls are a nice retro fit also. usually easier to add after the fact.
  7. BoilerMan

    BoilerMan Minister of Fire

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    I do not think it would work Rick. The pour-over idea that _dan had is my first inclination as well. If the subfloor can bear the added weight, or you can add some timber to it so it can.

    TS
  8. bpirger

    bpirger Minister of Fire

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    Great to hear from you Rick! How has the Garn been since the super cleaning?

    I agree that adding more on top is the best way....layout tubing and pour.

    Do you need to install any type of flooring over the concrete to meet any kind of USDA requirements or anything?

    Other thoughts: Could you cut tracks in the existing concrete for the tubing and install new flooring over the top? Or maybe repour the slots cut? Might help if the added height is troubling, though it may make the floor unstable (concrete cracking). Sounds like a cleaning intensive place...is that going to be an issue? Water through cracks/concrete or whatnot?
  9. Rick Stanley

    Rick Stanley Feeling the Heat

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    Bacteria trouble I had seems to be under control since I put the filter on.

    If I put the tubing on top of the existing floor would it be best to insulate on top of the slab and under the tubing to get the heat to go up into the rooms?

    The code only calls for the cement to be "sealed" and have drains for wash-down. Paint is all that they want for a sealer. The drains and plumbing are already there.

    Turns out there is only one layer of boards. The slab is 4" thick around the edges and pitched to 3" around the drains in the middle. The space is 20X40, 10X10 center beam, 10X10 posts 10' apart, joists are 3X9 (odd size) 16OC and 5x9 joists under the two load bearing walls, all rough sawn Pine.
  10. dogwood

    dogwood Minister of Fire

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    Rick, have you considered putting in some panel radiators instead so you wouldn't have to mess with the existing floor?
  11. Rick Stanley

    Rick Stanley Feeling the Heat

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    Don't know much about panels. I'm intrigued by radiant floor because I guess it can heat with lower temp water. Right? I have cast iron radiators in my house and they can do ok except for the coldest days with 140*. I was hoping I could do better than that on this other building.
  12. Bob Rohr

    Bob Rohr Minister of Fire

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    Keep in mind a 40X20 slab, 3-1/2" thick is about 9 yards of concrete, or about 36,000 lbs. You would want a structural engineer to bless that additional load on the framing supporting it.

    Ceiling or wall radiant is ideal for applications like this. You can home build ceiling panels from, copper, steel, aluminum, really any conductor that could hold water. Pex in transfer plates makes for a nice inexpensive ceiling radiant emitter.

    Still need to come up with a load number first, not all spaces can be heated with radiant panels regardless of where they are mounted.

    .
  13. Frozen Canuck

    Frozen Canuck Minister of Fire

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    Yes my concern would be too much dead load as well. FWIW Rick if you can take a fairly accurate drawing, photos & record the dimension & spacing of the framing members to a structural engineering firm in your area & get (for a couple of hundred dollars) an estimate of the load that floor will hold.

    Dimensionally framed floors usually don't BOOM fail, rather they fail over time as the grain in the wood frame is slowly pulled apart by too much load for the span & support. Starts as small cracks in the joist & goes from there usually.

    That's a lot of weight for the 16" O.C. floor you describe above. You may need to shore that floor up sooner rather than later. Also if you do another pour over to accommodate tubing the engineer can advise on how much additional support maybe required. As well as tell you how much live load you can add to the dead load.

    Cheap when you consider the cost of a replacement after failure.
  14. altmartion

    altmartion Feeling the Heat

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    they make panels just for this type of situation. I can't think of the manufacturer right now but I will dig around my office later. you can get it in 1/2 or 3/8 tubing and I think it was like 1/2 inch thick. I have never installed it but I know another contractor who has. he said he was happy with the ease of installation and the performance, but I never did get to ask how well it heated the room and not just the floor. hopefully I can find the stuff. I don't work out of my office much anymore.
  15. Bob Rohr

    Bob Rohr Minister of Fire

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    Look to the ceiling, I think your next heating project starts there. There are a bunch of products used for this application. They heat large aircraft hangers, gyms and other large spaces with high loads, with these products. This brand is available in the US. Or build your own.

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  16. altmartion

    altmartion Feeling the Heat

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    4 years ago i did building that is 80 by 180 free standing. it was designed to park and repair cranes and other heavy equipment. i put radiant in the floor and ceiling through the entire building except for a 20 by 30 office/ storage that was zoned by itself. i also had to put in 7 fan coils to help recover when they pulled in a frozen crane. the radiant above head feels great and works great. the recovery was much better than expected. it is very pricey to do and do it right. i am not sure how well it would work in a residential application, but i don't think it would have any negative effect. you may need closer spacing because of the load of the floor. if possible i would look into the ROTH radiant panels i mentioned in a previous post but couldn't remember the name. by now someone else must have something. maybe watts. they have some decent stuff and always seem to be on top of things in the radiant world. have you thought about electric floor radiant? watts makes stuff that has low amp draw and is a snap to install.
  17. tom in maine

    tom in maine Minister of Fire

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    The first thing is to know what the heat load is. And what temperature do you need to heat the building to, which affects the heat load.
    The thermal mass of the slab is going to store a reasonable amount of heat, which can be a help in the right situation.

    The slab is going to introduce some significant time lag.

    I think the staple up system is possible. More tubing per square foot would help, along with a fairly high insulation value underneath the
    tubing to ensure the heat goes in the right direction.

    Some math will save significant aggravation.
  18. altmartion

    altmartion Feeling the Heat

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    do you think it would be cost effective? i think it's going to take quite a bit of btu's to get it warm and maintain. that's a lot of floor so you would have to run high loop temps and probably plates. suspended won't work, at least i don't think it will. i am not sure how i could input the floor in my program. does yours have this option? i have a specific program that only does hydronics. maybe my wrightsoft does. that thing does a lot of stuff but is hard for me to use.
  19. Fred61

    Fred61 Minister of Fire

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    Heat stratifies in all materials, water, wood, concrete, whiskey, etc. I think it's possible to do with plates and a good amount of insulation below.
  20. altmartion

    altmartion Feeling the Heat

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    it may be possible but will it be cost effective? figure high water temps, probably very low flows. transfer plates are expensive too. it drives me crazy how much they cost. I would like to use them more but sometimes the customer won't go for the added cost. is the slab insulated around the perimeter? what are you planning for a finished floor if any?? do you have an extra inch to spare or would you have to raise doorways or anything. as mentioned by dog wood, modern panel rads are a nice low temp alternative. how about baseboard?
  21. tom in maine

    tom in maine Minister of Fire

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    I have no idea if it will be cost effective. You have to run the numbers to see how much heat the space requires. Then you can figure out how much energy you can get through the floor.
    www.builditsolar.com has got the heat load calculators if you do not know how to do it.
    If the heat load is not crazy high, it is probably do-able. And cost effective.
    It will need to be well insulated under the floor. No foil faced bubble wrap, real insulation!
  22. altmartion

    altmartion Feeling the Heat

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    you will 100% want foil as well. you want every bit of btu directed at the floor. the wood also works against in this situation. it doesn't even need to be reflective insulation, they make thin , ridged material to staple between the joists. then put as much batted insulation below it as possible without over stuffing the bay. and it wouldn't hurt to somehow seal all the bays with drywall or something to eliminate infiltration.

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