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Water supply temp for staple up and sandwich radiant floors

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by arbutus, Apr 8, 2013.

  1. arbutus

    arbutus Feeling the Heat

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    I'm trying to get a handle on typical values.

    What water supply temperature is typical?
    Has anyone seen any wild variations from published supply charts or are they pretty accurate?

    I'm calculating that I will need about 32 BTU/hr/sqft at design temperature.

    I was originally thinking about using staple up under the first floor, but the Uponor Appendix E and Zurn design manual shows that would require a water supply temperature somewhere around 180F!
    Joist Trak shows low 140s.
    A sandwich type system appears to require temperatures in the upper 140s or low 150s.

    That's for about half the total square footage that will be wood with an R value of .7 or so.
    I'll need a lower temperature for the other 50%, which is tile.


    Has anyone used Joist Trak? It looks like a quality product.

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  2. Bob Rohr

    Bob Rohr Minister of Fire

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    that is a high load for radiant alone, you may need to add some supplemental for design days. High 20's is reasonable for radiant floor with an 10- 82 surface temperature. Probably why you are seeing such a high supply number. Check the load carefully that sounds awfully high?
  3. arbutus

    arbutus Feeling the Heat

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    Hmmm.

    I built a spreadsheet. Here were the numbers I used. If you see anything abnormal I'd appreciate it.

    Outdoor design temp = -20
    Indoor design temp = 68
    Floor area = 768
    R 19 Wall area (no windows or doors) = 964 sq ft
    R 3 Window area = 62 sq ft
    R 2 Door area = 100 sq ft (patio slider, entry with side lights, and unheated garage service door)
    Delta T = 88

    Assume finished finished basement and upper floor are the same indoor temperature so no upward or downward losses.
    Structure loss = 10674 BTU/hr

    Air infiltration
    .75 ACH
    Volume = 7680 cu ft
    HC air = .018 BTU/cuft
    Delta T = 88

    Air infiltration loss = 9124 BTU/hr

    Total loss = 19798 BTU/hr

    Heated floor area = 80% or 615 sq ft (pretty close after subtracting stairway and kitchen cabinet areas)

    Required heat load = 32 BTU/hr/sqft


    Similar data (including an R32 ceiling and no doors) upstairs shows the load will be 25 BTU/hr/sqft.
  4. 4acrefarm

    4acrefarm Member

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    I have a staple up system with formed aluminum sheets (roof flashing). I run it around 120. works fine most of the time. Below 0 it has a hard time.
  5. arbutus

    arbutus Feeling the Heat

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    Thanks! Do you know what your heating load per square foot at 0F is? Do you have hardwood flooring?
  6. Bob Rohr

    Bob Rohr Minister of Fire

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    Here is what I come up with, .75 might be high for infiltration? 768 sq ft X 8 foot ceilings? = 6144 cubic feet.

    Attached Files:

  7. arbutus

    arbutus Feeling the Heat

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    Wow. Thank you Bob.

    I had figured 10 foot walls to include the joist space volume, both above and below the first floor.
    Is the joist volume typically neglected when calculating air changes?

    The house is average early 1990s construction. I plan to seal around outlets, fixtures floor penetrations and rim joist as best I can.
    I will be replacing the front door this summer, but the patio door and remaining windows are 22 year old wood framed Andersen casements.
    We do a lot of home cooking, and run the fan over the stove, as well as fans in the bathrooms for baths and showers.
    I figured 1 ACH was average existing construction.
    Maybe my efforts will bring that down to .5 ACH?

    The other thing I see is that my outdoor design temperature is negative 20F.
  8. rkusek

    rkusek Minister of Fire

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    Describe your install in detail. Did you make a jig to form the plates and how much do you have in them? 1/2 pex on 8" spacing? How did you insulate underneath? Did you seal the joist bays? I was almost ready to drywall my basement ceiling and rely solely on my forced air (W/A HX) that seems to work fairly well. I think something like what you have done will actually work well for me too because my heat load appears to be much less than I originally calculated kind of like the original poster. I like the idea of being able to keep the home warm during a power outage using only a battery/inverter setup.
  9. Bob Rohr

    Bob Rohr Minister of Fire

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    Yes the -20 makes a big difference, brings my calc to 18,000, with 10 foot ceilings. Is this a main level with a basement below? Heated below? Any floor insulation? I had the exposed ceiling (attic) at a R-16, maybe you have more insulation?

    www.pprbd.org has a free, manual load calc sheet
  10. flyingcow

    flyingcow Minister of Fire

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    I have staple up in only my kitchen area(25% of first floor sq/footage). I have baseboard all through the house. My staple runs about 130. I've got the typical two layers of plywood with tile floor. The staple up was put in mainly to keep the footsies warm. Does a nice job in the shoulder season.
  11. JP11

    JP11 Minister of Fire

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    I have staple up. No plates. One inch air space below, then 2" hard foil faced foam below.

    Runs 140 to maybe 150 if the tanks are really hot.

    Works great.

    JP
  12. arbutus

    arbutus Feeling the Heat

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    Thank you Bob.
    We're in the same ballpark then for heat loss numbers.

    I'm getting similar results to the calculator you linked as well.

    Creating my own calculator is helping me figure out what improvements are going to be most cost effective.

    The house is a two story on a full basement.
    Three bedrooms and two baths on the second story.
    The main floor is open from entry to kitchen to dining room and back to entry.
    There is an 8' basement what will be insulated and turned into finished living space.

    I am planning to go up to R32 blown in above the second story ceiling, after sealing the heck out of every ceiling and framing penetration I can locate.






    We close on the sale tomorrow morning. It is a foreclosure, and structurally in good shape, but we will be updating the interior.

    The current heat is existing baseboard. I don't like the blowing noise associated with forced air, and I really don't want to open
    I am planning on a wood boiler, but haven't ruled out a pellet boiler entirely, to act as our primary source of heat. Existing heat is electric baseboard.

    Since we will have the finish flooring up I'm planning on installing a sandwich type radiant floor in the second story bedrooms and bathrooms.
    We might do the same, or go with staple up below the first floor.
    Basement will probably be heated with a few panel radiators.

    I started another thread about boiler options and cost a couple weeks ago, and I'm CERTAIN I'll need more advice as we move forward.




    For the time being, published charts show it will work, and that's backed up by the success of several posters here, so I'm feeling good about the prospects for a successful install.
  13. Bob Rohr

    Bob Rohr Minister of Fire

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    Run the load calc after you upgrade insulation and make improvements. The structure drives the load, as you know. Spend the $$ on the upgrades. Consider floor coverings if you intend to run high supply temperatures.

    Grab a copy of the Radiant Flooring Guide from the Radiant Professional Alliance website.
  14. 4acrefarm

    4acrefarm Member

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    My house is a cape with a wing. The main first floor was the first project I purchased this setup from Radiant Supply in VT. 7/8" hose with soft plates purchased from them. These plates work very well. This section has hardwood floors, with iregular joist spacing so it was impossible to get as much hose as they recommended. when it is very cold 0 or less it has a hard time. The second section was the wing I tied to save money and bought roofing to make my own plates. I was to poor to alter my plan and used them anyway-mistake! It is harder to keep this wing up to temp. I have stapled perferated foil 2 ' down then fiberglass and then another layer of foil.
    Despite the shortcomings I have stated I am very happy with the system. it functions very well at 120 to 140 d . I keep improving the issulation under floor and it keeps getting better. I may spray foam under the wing section in the future.

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