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In-Joist, Hung Pex, Planning Manifold Connections

Eclipse
Eclipse Member Posts: 10
I'm using suspended Pex hangers beneath subfloor between 16" center 2x10" joists.  I'm using modular manifolds to distribute water, and trying to figure out how I get the Pex from the manifolds to the loops in my multiple loop zones.  My question has to do with the holes I need to drill to support my 4 zones - two zones have only one loop apiece, but the other two zones have 3 and 4 loops, respectively.



I've found many resources with advice on loop layouts and so forth.



What I've not found is much discussion of what / how many holes should be drilled to (1) support runs from distant loops back to the manifold and (2) from the manifold back to the zone's circulation pump in the mechanical room.



Some discussions presume you can run the supply of a loop through the same hole as the return from the end of the loop back to the manifold.  That says drill one hole in the joist while you're "in zone", looping supply through the joists and then run the return back through the same hole to the manifold.



Some discussions and diagrams indicate using a separate hole for the return run.



I understand both those, and appreciate at least some of the trade offs.



But - then how to get the supply of loop A to a distant area where the supply and return have to pass by loop B to get to the area A will heat?



Drill one hole and pass both supply and return for Loop A to get past Loop B?  My concern is that the Loop A supply would raise (via direct contact) the return temperature for the Loop B return, and so the manifold temperature drop would be less than true for the heated area.  Is that an issue?



Another alternative would be to route the supply for Loop A through the supply holes used by the intervening Loop B, and then let both returns come back through a second hole.  There'd still be some heat transfer among the returns, but surely not as much.



The literal translation, and I've seen some drawings suggesting this, is to dedicate two holes per loop - keeping supply and return separate for each loop.  Thus, I'd need four holes (but they could be smaller).



What is the "common wisdom" I'm not finding discussed elsewhere?



Thanks,

Comments

  • hot_rod
    hot_rod Member Posts: 22,024
    3/8 or 1/2' pex?

    "sew" it through the joist. Take the free end down through 2-3/8" holes, turn around and come back to the manifold.



    Fasten that end solid at the manifold. Put a screw right trrough the pex to a joist so you don't yank the manifold.



    Then pull the loop down to the end of every joist bay, fasten the loop end and work back to the coil.



    You need to calculate how many bays your loop length will cover so you start in the right bay.



    If you have multiple loops, start at the one most remote.



    You may need to drill a few sets of holes, depending on how many loops.



    Some fasten the runs below the joist instead of drilling holes, looks cheesy to me.



    If you have TJIs you need to refer to the hole drilling chart to see where you are allowed to drill, same with joists. You need to be a certain distance from the bearing point for the holes.



    Google that hole size and drilling location for whatever joist you have.





    goes better with two people to prevent kinking.i
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    RobG
  • Eclipse
    Eclipse Member Posts: 10
    Thx, Hot Rod

    "You may need to drill a few sets of holes, depending on how many loops".



    That, is the question.



    How many holes in each joist along the near zone, to accommodate the far zone supply and return?  One hole for the far zone supply and return to share, or two holes, one each?



    What I'm really asking is whether heat transfer from the far zone supply tube to the far zone return tube is great enough, if they share a route through a single series of holes in joists they traverse to get back to the manifold, to disrupt accurate balancing of the far zone?



    Eclipse
  • hot_rod
    hot_rod Member Posts: 22,024
    3 loops

    would require 3 sets of holes, space them 12 or 16" o.c. or whatever the design calls for.



    So the first loop traveling the farthest may only cover two bays, the 2nd loop three bays, maybe 3 bays for the 3 rd loop.



    The loops need to be the same length, sometimes a loop only goes part way down a bay, before you need to head back to the manifold so as not to exceed the loop length.

    Bring the next loop to meet that end. In that case drill another hole at the other end of that joist bay, bring the next loop down to meet the shorted one.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Eclipse
    Eclipse Member Posts: 10
    re: 3 loops

    That's the question I was asking, and that's the answer I've been wondering about.



    By 3 sets of holes, you mean 2 holes per loop (6 in this case), or one per loop (3)?  Based on your first answer, I think you mean 2 holes per loop at the main end (not including those at the other end to complete a short run up a joist space), so 6 total.



    I'm using 1/2" ID PEX - so I planed to use 1 3/8" holes to accommodate 2 tubes per hole (supply and return for one loop).  Why are you calling out 2 3/8" holes? or do you mean two 3/8" holes?  I've been given the advice to use the smallest holes that easily accommodate how ever many tubes must traverse the hole, so as to minimize damage to the joists ...



    Thanks again.
  • hot_rod
    hot_rod Member Posts: 22,024
    edited August 2014
    depends on how many

    joists you are pulling down through. 1-3/8 can be tough to pull more than 4-5 joists, so I used 2-3/8" holes. as long as the joist dimension allows it.



    The only time you need to drill the far end is if you come up short. Then the next loop needs to go down the the far end, cross over to fill that bay.



    Here is a link for hole drilling in structural joists. Check with your local codes, generally a 2-3/8 inch hole can be drilled in 2X8 or deeper joists, stay out of the middle 1/3rd.





    http://www.qis-tx.com/newsletter.0605.asp





    If you have engineered TJI type joists, use their hole drilling guide lines.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Eclipse
    Eclipse Member Posts: 10
    re: Depends on ...

    Good point.  Thanks for the guidance.
  • Eclipse
    Eclipse Member Posts: 10
    Followup for the record

    I wound up using 1 1/2" self feeding drill bit (aggressive) for my holes, and having the return of each zone share the hole with its supply. I figured within the zone, there would not be enough heat transfer between the supply and the return to matter.

    However, I also had the supply and return share the holes from the manifold (centrally mounted in the house) to the zone loop entry/exit, and I think I see evidence of heat transfer in the manifold supply/return temperatures of one of my three zones.

    The central zone (four loops each about 300' in length, 1/2 inch ID ox-barrier PEX) in my home is the largest and is flanked on both sides by other zones. As a result, it's more isolated from exterior temperatures. Interestingly enough, its supply and return temperatures read about the same on the manifold thermometers, which suggests there's no delta-T occurring, but the zone is maintaining it's temperature just fine in 20 degree external temperature weather. My conclusion is that this zone may be seeing heat transfer from supply to return loop ends on the transit back to the manifold, resulting in the small delta T reading. I suspect the loops ARE seeing delta-T - because the zone temperature is fine - but that the reading of the return loop temperature at the manifold is falsely high due to transfer on the leg back from the zone loop entry due to sharing joist holes.

    Other observations:

    I tried to use a 1 3/8" bit (Forstner), but gave up early in the project and switched to the 1 1/2" self-feed style, which worked well with a heavy-duty hole-hog drill.

    I didn't quite realize how much work remained after the holes were drilled, tube was strung and stapled up. Hanging insulation (even the radiant barrier style I used) was more work that I expected.

    I lost 20 pounds installing the system in September. Not bad, and appreciated.

    Now that cold weather has well and truly arrived, I'm adjusting boiler settings to increase cycle run times, and planning to add attic insulation.
  • hot_rod
    hot_rod Member Posts: 22,024
    Yeah, drilling and pulling overhead is a tough job. Keeping the bit sharp helps a lot. A small file keeps them razor sharp and keep a spare drill feed point for the bit. That pulls the bit, no need to push the drill
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Rich_49
    Rich_49 Member Posts: 2,766
    Shoulda followed Rod's 2 3/8 suggestion . Now there is no room for the pex to expand to the rear of the hole . You'll likely have noise .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Ironman
    Ironman Member Posts: 7,367
    Eclipse said:

    Followup for the record

    I wound up using 1 1/2" self feeding drill bit (aggressive) for my holes, and having the return of each zone share the hole with its supply. I figured within the zone, there would not be enough heat transfer between the supply and the return to matter.

    However, I also had the supply and return share the holes from the manifold (centrally mounted in the house) to the zone loop entry/exit, and I think I see evidence of heat transfer in the manifold supply/return temperatures of one of my three zones.

    The central zone (four loops each about 300' in length, 1/2 inch ID ox-barrier PEX) in my home is the largest and is flanked on both sides by other zones. As a result, it's more isolated from exterior temperatures. Interestingly enough, its supply and return temperatures read about the same on the manifold thermometers, which suggests there's no delta-T occurring, but the zone is maintaining it's temperature just fine in 20 degree external temperature weather. My conclusion is that this zone may be seeing heat transfer from supply to return loop ends on the transit back to the manifold, resulting in the small delta T reading. I suspect the loops ARE seeing delta-T - because the zone temperature is fine - but that the reading of the return loop temperature at the manifold is falsely high due to transfer on the leg back from the zone loop entry due to sharing joist holes.

    Other observations:

    I tried to use a 1 3/8" bit (Forstner), but gave up early in the project and switched to the 1 1/2" self-feed style, which worked well with a heavy-duty hole-hog drill.

    I didn't quite realize how much work remained after the holes were drilled, tube was strung and stapled up. Hanging insulation (even the radiant barrier style I used) was more work that I expected.

    I lost 20 pounds installing the system in September. Not bad, and appreciated.

    Now that cold weather has well and truly arrived, I'm adjusting boiler settings to increase cycle run times, and planning to add attic insulation.

    Did you use heat transfer plates?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Eclipse
    Eclipse Member Posts: 10
    edited February 2015
    Rich said:

    Shoulda followed Rod's 2 3/8 suggestion . Now there is no room for the pex to expand to the rear of the hole . You'll likely have noise .

    Into the dead of winter, and no - no noise from the PEX tubes expansion. 1 1/2" appears to have been sufficient, given the turns and tubing I was using (Zurn hy-PE-RTube 1/2" 5-layer).
  • Eclipse
    Eclipse Member Posts: 10
    Ironman said:

    Eclipse said:

    Followup for the record

    Did you use heat transfer plates?

    No, I didn't. Used stand-off Peter Mangone PEX tubing clips, with a pneumatic RB6 gun (rented for the install). Then hung rFoil reflective insulation (2200 Series) Metalized Foil Barrier (double layer of polyethylene bubbles sandwiched between two radian barrier metalized sheets).

    Gave up trying to staple up the foil to within 3 inches of the subfloor between the joists, and for the most part, stapled up creating about a 6" box below the subfloor - so more airspace, less chance of barrier contact with PEX, and that's working out well. I did NOT tape the sides of the foil to the joists, and yes, you can see heat leaking out at the staples, but it's sufficient for what I need, and I can use the heat loss into the basement, since it's used for storage and some exercise equipment that gets too little use.
  • Eclipse
    Eclipse Member Posts: 10
    The house had only about R-10 insulation in the attic - 2" bat of pink fiberglass and about 2" of compressed (by now) blown cellulose. We suspected we needed more to contain heat loss, and boy were we right.

    I went through several stages as the winter came on:

    1) base install, leaving boiler and mixing valves at default settings, which were boiler high temp set to 165 or so, and mixing valve on the circulating board around 118.

    2) That default setting was fine for keeping rooms at thermostat setting (70) down to about 20-25 degrees (F), but below 25, room temps dropped. When outdoor temp dropped to 5-10 degrees, the indoor rooms were down to 64 and I knew I need to make adjustments.

    3) Read the boiler manual and set the high temp limit to 180, figuring that would let the boiler run longer when it kicked in. Also lowered the low temp setting to 160. Observations show the boiler tank temperature dropping to 150 or so by the time the boiler kicks in - I don't want to let it drop much below that.

    That helped make the boiler run cycles longer, but after talking to my supplier, also raised the temperature of the water circulated to the PEX, from 118 or so towards 130.

    That combination has been enough to let the house, even with the lousy attic insulation, hold the 70 room temp until temps get to 10-15 degrees. Below that, though, and room temps dropped to 68 or so - still better, but one room (master bedroom, of course), was more like 64.

    4) Did the attic thing - blew in 15 inches or so of cellulose insulation (after spending two weeks building a catwalk out of 2x12s and 24" wide plywood to get from Garage access to attic A/C air blower, building baffle walls around garage we didn't need to insulate, and inserting vent baffles).

    At this point, the house holds room temp target of 70 down to 0 degrees outside, and I'm seeing reasonable boiler cycles, I think - boiler run hours is showing about 11-14 hrs per day (generally 33-45% run hours / clock hours), seeing cycles of 4-5 cycles per clock hour, and I'm burning 6-7 ccf natural gas per day with 65 degree heating degree days in the 40-61 range. Sun loading from sunny (vs snowy) days makes a big difference in how many degree-days / gas ccf (6-8 degree days per ccf for snowy days, 8-10 degree days per ccf for sunny days).

    So, I'm fairly pleased with what I'm seeing.

    Next question is - should I invest in an outdoor reset module for the boiler.

    And to review my setup:

    Boiler: Crown AWR-70 (50k BTU/hr) cast iron boiler, 88% efficiency rating,
    House: 1961 construction, brick wall ranch, 1850 sq feet, of which 250 or so is over crawl space and rest is over full course cinderblock unfinished basement

    NYCERDA energy audit shows house walls ARE insulated.

    Fun!
  • Eclipse
    Eclipse Member Posts: 10
    edited February 2015
    Eclipse said:

    The house had only about R-10 insulation in the attic - 2" bat of pink fiberglass and about 2" of compressed (by now) blown cellulose. We suspected we needed more to contain heat loss, and boy were we right.

    Objective of the blown in insulation was raise presumed R-10 attic insulation to more like R-50 or R-55. Just didn't think we had enough room to go all the way to R-60, which would have required more like 18" blown in (low pitched roof).

  • hot_rod
    hot_rod Member Posts: 22,024
    Eclipse said:

    The house had only about R-10 insulation in the attic - 2" bat of pink fiberglass and about 2" of compressed (by now) blown cellulose. We suspected we needed more to contain heat loss, and boy were we right.

    I went through several stages as the winter came on:

    1) base install, leaving boiler and mixing valves at default settings, which were boiler high temp set to 165 or so, and mixing valve on the circulating board around 118.

    2) That default setting was fine for keeping rooms at thermostat setting (70) down to about 20-25 degrees (F), but below 25, room temps dropped. When outdoor temp dropped to 5-10 degrees, the indoor rooms were down to 64 and I knew I need to make adjustments.

    3) Read the boiler manual and set the high temp limit to 180, figuring that would let the boiler run longer when it kicked in. Also lowered the low temp setting to 160. Observations show the boiler tank temperature dropping to 150 or so by the time the boiler kicks in - I don't want to let it drop much below that.

    That helped make the boiler run cycles longer, but after talking to my supplier, also raised the temperature of the water circulated to the PEX, from 118 or so towards 130.

    That combination has been enough to let the house, even with the lousy attic insulation, hold the 70 room temp until temps get to 10-15 degrees. Below that, though, and room temps dropped to 68 or so - still better, but one room (master bedroom, of course), was more like 64.

    4) Did the attic thing - blew in 15 inches or so of cellulose insulation (after spending two weeks building a catwalk out of 2x12s and 24" wide plywood to get from Garage access to attic A/C air blower, building baffle walls around garage we didn't need to insulate, and inserting vent baffles).

    At this point, the house holds room temp target of 70 down to 0 degrees outside, and I'm seeing reasonable boiler cycles, I think - boiler run hours is showing about 11-14 hrs per day (generally 33-45% run hours / clock hours), seeing cycles of 4-5 cycles per clock hour, and I'm burning 6-7 ccf natural gas per day with 65 degree heating degree days in the 40-61 range. Sun loading from sunny (vs snowy) days makes a big difference in how many degree-days / gas ccf (6-8 degree days per ccf for snowy days, 8-10 degree days per ccf for sunny days).

    So, I'm fairly pleased with what I'm seeing.

    Next question is - should I invest in an outdoor reset module for the boiler.

    And to review my setup:

    Boiler: Crown AWR-70 (50k BTU/hr) cast iron boiler, 88% efficiency rating,
    House: 1961 construction, brick wall ranch, 1850 sq feet, of which 250 or so is over crawl space and rest is over full course cinderblock unfinished basement

    NYCERDA energy audit shows house walls ARE insulated.

    Fun!

    If the boiler cycles off, on design or below design days, and the rooms are not maintaining desired temperatures, that may indicated not enough heat emitters or energy transfer.

    Constipated Distribution, a term I learned from Radiant Engineering the manufacturer of transfer plates :)

    Sometimes increasing the supply temperature in that type of tube installation will get you over the hump. No doubt a properly installed and adjusted ODR would automate some of the temperature modulation.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Eclipse
    Eclipse Member Posts: 10
    edited February 2015
    hot rod said:


    Eclipse said:


    Next question is - should I invest in an outdoor reset module for the boiler.

    Sometimes increasing the supply temperature in that type of tube installation will get you over the hump. No doubt a properly installed and adjusted ODR would automate some of the temperature modulation.

    Thanks, Hot Rod - the cost for my boiler seems to be about $[deleted] for parts, and I'm going to have to decide how much automation I care to pay for.

    Edit: deleted mentioned cost - sorry.
  • hot_rod
    hot_rod Member Posts: 22,024
    one step at a time
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream