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copper tube sizing

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I have 1/2 pex in my garage floor attached to a Distribution panel purchased from Menards, I have a Stiebel Eltron electric boiler that I am about to connect to the panel..
Question is: the Panel inlet and outlet(s) are 3/4" as is the Boiler, I have enough 1/2" copper tubing lying around to make all of the connections between the two units, will that work well? or will I lose heating capacity by doing so?

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
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    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,106
    edited October 2023
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    You should be fine as long as you don't need more than 12,000 BTU's to heat the garage.

    What's the distance between the boiler and tubing connections?

    Follow boiler piping instructions and insulate all the exposed pipes.
    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
  • hot_rod
    hot_rod Member Posts: 22,476
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    What size is the electric boiler? What is the heat load for the garage?
    Or how many 1/2" loops at what length?
    Typically you design for around 1/2 gpm per loop of 1/2" pex

    So 3 loops would need around 1.5 gpm.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • polarguy
    polarguy Member Posts: 8
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    Thanks, I have an electric hydro shark 19.6kw boiler rated at 65525 btu, per literature
  • polarguy
    polarguy Member Posts: 8
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    Also to answer your question, the boiler is less than 3ft from the panel, and yes I will insulate that distance.
  • GroundUp
    GroundUp Member Posts: 1,956
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    1. Stiebel Eltron does not make a boiler- you have a water heater that Hydro Smart put a boiler sticker on.
    2. Even 3/4" is too small for 19.6kw
    3. How many loops and how long are they?
    4. What are the dimensions of the garage and where are you located?
    bburd
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
    edited October 2023
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    There are limiting factors in selecting a boiler, and in installing radiant floor heat.

    The dimension of the floor is the limiting factor in selecting the amount of tubing and how much heat that will put into the building. Say it is a 2 car residential garage. at about 24 x 24. If you put the tubing at 6" spacing there will be over 1200 feet of tubing. If you selected 12" spacing then there will be about 600 feet of tubing.

    Take the middle number of 800 feet of tubing. Make that 4 loops at 200 feet each. You will need to move the water at about 1/2 GPM per loop or a total of 2 GPM.

    1/2" is good for that with the right pump. But if you want to select a boiler for that small job, you don't need 20 kW. You don't even need 10 kW. You could use a small under the counter water heater that will have a few gallons of storage. That will act like a buffer tank to reduce short cycling of the electrical relays and thermostats. A water heater is actually a better choice for such a small job. (I don't believe I said that) :D

    If you are thinking of adding more floor heat in other places then that is a different story.

    SO... How big is you project. Do you have more that just a 2 car garage? If YES. then you will need 3/4" tubing to connect from the boiler to the manifold. 5 loops or more will require at least that. more that 8 or 9 loops will require 1" pipe. Yea... 1" is bigger that the heater openings.. but that is how boilers work. Water heaters move water faster with more noise in the pipes. Boilers can not be so noisy ...so we need bigger pipes to move the same amount of water slowly.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • polarguy
    polarguy Member Posts: 8
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    Ok,
    Garage is 40'x48'
    6 loops 1/2" pex roughly 9" apart 285' to 305' in length
    ST. Paul MN
  • hot_rod
    hot_rod Member Posts: 22,476
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    3/4 copper would be best
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GroundUp
    GroundUp Member Posts: 1,956
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    3/4 copper would NOT be best. For 67,000 BTU 3/4" is too small to maintain a decent delta T. 1" is a little overkill, but there is not an in-between option for copper. That whole Hydro-Smart panel is inadequate for that water heater- the pipe is too small as is the primary pump. If 1" copper isn't an option, run 1" barrier pex for all the connections you have to make. Or send the whole thing back to Menards and buy something that'll actually work well. I take at least a dozen of these junk piles out of service annually, but if you want to do your own research, check out HydroSmart's reviews. The owner has been sued countless times and just keeps changing the name to stay in business. They're in Elk River, just a short jaunt up HWY 10 for you.

    Side note, 19.6 kw is also much too big for that building if there is any amount of insulation at all. Most 2000 SF new builds that I install get 12-15kw boilers, which ironically are usually cheaper than what you have and you don't have to assemble them.

    EdTheHeaterMan
  • polarguy
    polarguy Member Posts: 8
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    So, If i'm reading you correctly, you are suggesting that while 3/4" would be an improvement over 1/2" 1" is the better way to go? the 2 circulation pumps have a low-medium-high speed switch which I believe tops out at 17 GPM, Again would I assume to set them on high?
  • polarguy
    polarguy Member Posts: 8
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    And yes, I have 2" of pink insulation under and on the sides of the 7" slab..
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,167
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    Remember the limiting factor thing I mentioned earlier. @GroundUp indicated that you need 1" to move 67,000 BTU out of the boiler. However there is still the limiting factor of six 1/2" loops. the most water you can put in any one of those loops is 1-1/2 GPM. But you are more than likely going to put 3/4 to 1/2 GPM thru those loops. six loops @ 3/4 GPM = 4.5 GPM and a 3/4" pipe from the boiler to the manifold should be just fine. I believe that you will only use about 40,000 to 45,000 BTUh of the 67,000 available BTUh the boiler has to offer. So 1/2" will not work for you and 1" would be better in order to get the water from the boiler to the manifold with less friction and perhaps less noise, I believe that 3/4" WILL WORK just fine.

    Since you need to purchase the pipe because you don't have "More than enough laying around" I would look at the cost of both 1" and 3/4" to see if there is a huge difference. If it is less than $50.00 difference, I might suggest 1"

    BUT 3/4" will work for your situation.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    hot_rod
  • GroundUp
    GroundUp Member Posts: 1,956
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    I did not say that 3/4" would not work. I said it is not the "best" as somebody else indicated, which is an indisputable fact.

    The circulators that you have are 15-58s, and they would only achieve 17GPM on high if there were zero resistance in the piping (aka zero piping). You will have approximately 7 psi of resistance using straight water, meaning that circulator on high speed with 3/4" copper piping would only flow around 2 GPM through the tankless water heater and "integrator panel" that you have. If you add glycol (which you should, given the location and high probability of system failure), that will drop closer to 1.5 GPM. Those Stiebel water heaters do not modulate, so you will have a constant 65-70 degree delta through your system to keep it from short cycling (which is well known to cause fires with those units, hence many of the lawsuits) and that means a drastic variation in floor temperatures.

    A real boiler could be used with that integrator panel without issue, but you would be money and much aggravation ahead to return everything you have to Menards and start over with a real boiler from Electro Industries in Monticello. Or if you have Facebook, there is a guy on Marketplace near Foley who sells complete plug and play panels using those Electro boilers for a similar price to what you've got invested in this system that isn't ever going to work well.
  • polarguy
    polarguy Member Posts: 8
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    I appreciate all comments and suggestions, this has been very helpful, My son who works with piping equipment, came over last night with all the 1" stainless piping required to connect the boiler to the panel..
    Is there an issue with stainless vs copper?
    Also it appears to me that my unit does modulate: KW modulation range: 1 KW - 19.2KW (per website)
  • polarguy
    polarguy Member Posts: 8
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    Any thoughts on Copper v stainless?
  • hot_rod
    hot_rod Member Posts: 22,476
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    stainless if fine, it will look and perform well.

    as I see it 7 psi = 16' head. the Grundfos 15-58 on speed 3 will move about 4 gpm at that head.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream