Vermont Am I crazy to think that I can heat my house using staple up with geo?

Discussion in 'General Discussions' started by Grant, Mar 21, 2015.

  1. Grant

    Grant New Member

    What btu/ft^2 can I expect for 3/4" PEX 8" OC staple up w/o plates for 110 degree supply? What would plates add? Is there a curve showing effect of temperature for this type of installation?

    I am beginning to think that I made a bad choice when I added the geo system and using staple up. Original house used primarily wood heat with a gas force air backup. We were putting on additions to move our primary living space to all on one floor and wanted to update our heating system with the additions. Due to my wife's allergies we wanted to get away from forced air and wood heat, radiant sounded real good. We split the system into 2 pieces, one 4 ton water to water for the 1st floor radiant and one 2 ton water to air for 2nd floor heating and general A/C. All the information that I had at the time sounded like staple up would work for the 1st floor.

    I chose staple up as the original drawings had been drawn for forced air with all the floors being on the same level. I looked at warm board, but that was very expensive and required changing foundation heights and considered gypcrete, but that would have meant changing all the floor heights. The engineer involved recommended the staple up and not using plates. So what I have is 3/4" PEX 8" OC, 2 runs per 16 OC bays, except one part of the house where I ended up 12" OC joists so the PEX is 3/4" 6" OC. Under the PEX I have foil bubble wrap insulation. Installation of all of the loops has been not been completed, something that I do when I am not working on other portions of the construction, and the duct work from the water to air unit to the risers has not been completed. I am 85% complete with all of the loops and in rooms where I am totally completed we find that they are not able to maintain temperature creating my doubts about the configuration. I keep telling myself that when everything is installed it will heat better. Am I crazy?

    With the additions I insulated like crazy to reduce the load as much was reasonable. New windows every where and 2x6 walls sheathed with Zip R to reduce bridging and insulated with 5" of foam. New foundation insulated with 3" foam on the outside and the existing foundation still exposed to the ground insulated with 3" foam on the inside. Roof was sprayed with a minimum of 8"++ of foam and where feasible I had them overspray the rafters with at least 1" of foam to reduce bridging. It looked like an igloo when we got done. I have a detailed room by room heat loss study so I know what I need for heat per square foot by room. What can I expect for heating per ft square for 3/4" PEX 8" OC at 110 degrees?

    Rather long winded, but thanks in advance for any responses.

  2. Bergy

    Bergy Member Industry Professional Forum Leader

    What flooring is above the staple-up? Bubble foil is, for all practical purposes, worthless. Remember one thing... Heat goes to cold. if it's easier for the heat to go down, it will.

  3. Grant

    Grant New Member

    3/4" subfloor with 3/4" hardwood glued and stapled
  4. Bergy

    Bergy Member Industry Professional Forum Leader

    110* without plates and bubble foil, I doubt it. With plates and good insulation, maybe...
  5. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Plates are helpful in spreading the heat throughout the joist bay. There needs to be more R-value under the staple-up than above it. Most manufacturers want a 2" air space between the insulation and the bottom of the sub floor.

    Want is the delta T through the loops? Are you using a buffering tank between the water to water and the floors?

  6. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    It certainly can and may be even should work, just not as efficient as it is possible. You engineer might not understand that the higher the supply temperatures are, the lesser efficient the geo system is.

    Usually you loose about 15% efficiency for every 10 degrees higher supply temperature.

    Having said that you have to focus now on making your distribution system more efficient. Yes, when you are done with the whole house your system should work better. You can always retrofit plates, increase your supply temperature to about 120F, increase your flow to decrease your delta T and increase your average supply temperature, and install an outdoor reset to lower the temperatures when you don't need it. I second the question if you have a buffer tank installed.
  7. BadgerBoilerMN

    BadgerBoilerMN New Member

    You are not crazy, just misinformed.

    Anyone that advocates 3/4" PEX for sub-floor installations in residential construction is also woefully ignorant and should be avoided.

    Every successful radiant floor heating job starts with a proper heat load, or an informed guess. The required output is determined and then manufacturer's data is used to determine if the radiant emitter you have chosen will meet the heat load required by the room you are trying to heat. In most construction in most cold climates extruded aluminum plates driven by 1/2" PEX will suffice. This is especially true when the relatively low temperatures available from ground source heat pumps.

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