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Underfloor PEX Plate advise

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Comments

  • RetrosPex
    RetrosPex Member Posts: 56
    Dave H2

    Sorry, I disagree with your disagreement. :)
    The power consumed to overcome the static head in a pumping system varies linearly with flow, and not much can be done to change that. There are opportunities to reduce the power required to overcome the friction, such as varying the tube dimension, albeit at a higher initial cost. The actual static head varies depending on flow rate, pipe size, texture, etc.

    It takes less energy to pump a fluid through a 1/2 tube than through a 3/8" tube. You are correct, the BTU requirement will be delivered either way. There is the issue, which could vary regionally, of what tubing is normally stocked. Overwhelmingly, the standards are 1/2, 3/4, 1". There used to be 5/8, and of course there is 3/8. In my personal experience, it is usually beneficial to be able to run a 300' loop, versus a shorter length. It depends on the room dimensions, but for example, the last room I did ended up at 290' per loop, and we did 3 loops, leaving 30' on a 1000' roll. 30' is a nice use-able chunk of tubing.

    I didn't mean that I've never seen 3/8" tubing, I have. I've never seen a project that used it. In the few instances I've seen 3/8" tubing for sale, it cost more than 1/2".

    Most of the plates I run into are for 1/2 tubing also.

    Maybe that is just where I'm located, which is the Midwest.

    Also, I think it is a mistake to pick a pump out in advance that you are going to use for a job, and make the tubing and plates fit the pump. Get the best, most effective tube/plate solution, and then buy the pump. Personally, I have just purchased Grundfos Alpha 2 pumps, although I have several 15-58s on the shelf. Another thing I do, if the run of tubing has a considerable distance to travel just to get to the load, I start out with larger dimension tubing, I often pick up sales on 3/4' tubing, and always have it on hand. To each his own.



  • Ironman
    Ironman Member Posts: 7,375
    "It takes less energy to pump a fluid through a 1/2 tube than through a 3/8" tube."

    That would totally depend upon the length of each tube.

    When using 3/8" tubing, the lengths of each loop are kept shorter than with 1/2" and more are added as necessary to get the required gpm. When the head and the gpm are the same for both size tubing, then the electrical consumption of the pump will be the same.

    Sorry, but Dave is right. I wouldn't argue with him about pumps; that's his bread and butter.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Canuckerrick in Alaska
  • hot_rod
    hot_rod Member Posts: 22,120
    I'd add with ECM technology power consumption becomes a non issue. A 37W circulator will pump 200- 225' 3/8 loops without an issue. Most all the aluminum plates are available as 3/8 or 1/2.

    A lot of the wood dry systems use 3/8, and Upon and Viega still offer 5/16" tube for their over the top, dry systems.

    Or the new Mr Pex transfer plates that accepts both. Must still be a market for 3/8?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TAG
    TAG Member Posts: 755
    Really want to thank everybody for taking the time to advise me on this. Guess I'm guilty of the "Always did it that way" not that I have done that many. Like to do my research and not be afraid of trying a different path. I will not have many stud bays to bring the tubing down .. the 3/8 is so much easier to manipulate.

    I'm going to the property Sunday -- to map it out.
  • TAG
    TAG Member Posts: 755
    Spent some time at the house yesterday. The upper most room has a floor 28' 6" wide ...20 bays long.

    If I use either 6x4' or 3x8' plates -- that leaves me 4.5 feet for playing around at each end and some plate separation -- so I need 240 4' plates.

    The rest of that floor is only 10' 6 wide -- so 2x4' or one 8'. I have 21 bays. 84 plates.

    Think the 3/8 PEX is the way to go -- there is stuff to work around and the smaller tubing is better,
  • kenjohnson
    kenjohnson Member Posts: 85
    The "thick" aluminum plates are easy to cut with an angle grinder. After cutting, I deburred the cut edges with a round or straight file so it wouldn't cut me or the pipe. By cutting to size, you can fit more plates in and run with a lower water temperature.
  • Gordy
    Gordy Member Posts: 9,546
    edited March 2019
    Better Yet, if you have a miter saw, and a 96- 120 tooth blade for aluminum perfect cuts with little de burring , and much safer.
  • hot_rod
    hot_rod Member Posts: 22,120
    if I need a bunch of them cut, I leave them in the box and cut plates and box with a 10 miter saw, non ferrous blade

    A Unibit in a cordless drill deburrs and bevels the ends of the channel
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    rick in Alaska
  • TAG
    TAG Member Posts: 755
    I'm not thinking I need to cut any .... If I stop 2' from each end that should allow room for the loop and about an inch between plates. Even if I increase the plate spacing I still have 18" for the loop at each end.
  • rick in Alaska
    rick in Alaska Member Posts: 1,457
    I have a job where I sold the 3/8 tube and plates to the customer and he installed it. I hooked up all the manifolds and boiler, and used 15-42 pumps on it, and it has been working just fine now for about 15 years . If I had to do a staple up situation, which I hope to never have to, then it would definitely be 3/8 tube.
    And I agree with the others. 10 feet of head through either 3/8 tube of 1/2 inch tube, will cost the same in pumping costs. Sure, you might have to increase the manifold by a loop or two, but to me having to fight that tube over your head, it would be worth it.
    Rick
  • TAG
    TAG Member Posts: 755
    edited August 2020

    Thank's all -- Following advise here I went with the 3/8 tubing (Viega) and the heavy (Thermofin) plates. Contractor did a very nice install. Had supplied plates and two rolls of 1200'. They went on the safe side and kept the loops down in the sub 170' length. Went from my estimated 7 loops to 11. See picture.

    Earlier in this thread Dave H_2 made a statement that using 1GPM flow you get a head of 5.22 -- that was with 200' loops of 3/8 tubing. Guess with 7 loops?

    I'm still confused by the pump needs on this project. Not sure if I need a dedicated pump for this manifold. Can I still use a 1" manifold w/ 11 loops of 3/8. The remote feed from the boiler in mechanical room is 1 1/4 copper.

    Mentioned previously. Rebuilding my converted church after a major fire. This retrofit radiant is for the uppermost great 1000sf room -- the worst case heat loss is about 20k ... but, it's open to other levels bellow .. so I think this is high. The house will also have heat supplied by the ducted system that I put in for AC if needed.

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,002
    "Earlier in this thread Dave H_2 made a statement that using 1GPM flow you get a head of 5.22....."

    I would try and stay around .3 gpm per loop which will give you 3.4 feet of head. At 1 gpm, you're off the charts; 30 feet of head or more.

    If you flow .3 gpm per loop and have 11 loops, the total flow is 3.3 gpm which can be easily supplied with a 3/4" copper supply line.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    Zman
  • Zman
    Zman Member Posts: 7,569
    edited August 2020
    Alan (California Radiant) Forbes said:

    "Earlier in this thread Dave H_2 made a statement that using 1GPM flow you get a head of 5.22....."

    I would try and stay around .3 gpm per loop which will give you 3.4 feet of head. At 1 gpm, you're off the charts; 30 feet of head or more.

    If you flow .3 gpm per loop and have 11 loops, the total flow is 3.3 gpm which can be easily supplied with a 3/4" copper supply line.
    Like he said...

    You have done a nice job with the low resistance, low temp design. This shows you flow rates with an inexpensive common grundfos 15-58 on speed 1. The nice part of a 3 speed or delta p circ is that you can turn it up a speed if you have some unexpected resistance along the way.

    Unless you have other zones with similar resistance characteristics, a dedicated circ is a good idea.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • TAG
    TAG Member Posts: 755
    Zman -- what is driving the calculation ? That's a cool program. Do you dial in the desired gpm .. and it gives the rest?

    What I had to do is run a 1 1/4 cu line from the mechanical room to the middle of the stone building. about 25' away. This CU line will supply the manifold with 11 loops for the plates .... it also will do another 7 loop manifold for the 1/2" PALP of Warmboard. 200' loops. Back in the mechanical room I have another 5 loops of Warmboard and 8 loop slab. I'm trying to limit the pumps if possible ... I know the old way would be 4 pumps. There was no way to run all the loops back to the mechanical room (no space) ...Plus it increased the pipe length.

    If I need a dedicated pump for the 11 loop plate manifold -- would not a constant pressure pump be better vs a 3 speed .... or am I over thinking.
  • Zman
    Zman Member Posts: 7,569
    The program allows you to input the characteristics of the loop and then toggle between pumps until you get the flows you want.

    For your system, maybe you would be better off with 1 larger delta P circ and balancing valves on the zones.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein

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