75' Pex Run - Home Run vs. Remote Manifold

How would you plumb it?

  • Home Run - 3/4" PEX

    Votes: 1 100.0%
  • Home Run - 1/2" PEX

    Votes: 0 0.0%
  • Home Run - 3/8" PEX

    Votes: 0 0.0%
  • Remote Manifold - 1" Supply

    Votes: 0 0.0%
  • Remote Manifold - 3/4" Supply

    Votes: 0 0.0%
  • None of the Above

    Votes: 0 0.0%

  • Total voters
    1

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I'm replacing the original supply pipes in a 95 y/o house and am looking for some advice given the inefficient location of the boiler (which provides the hot water) and fixtures (kitty corner from one another).

There are 23 fixture units, the farthest being 75' from the boiler, though most fixtures are not significantly closer than this. There will likely be front and rear irrigation added in the future, which I believe would up the fixture units by 5.

Given the long run lengths, what's the most efficient setup in this scenario, which will prevent pressure drops while running multiple fixtures AND get hot water there the quickest?
 

Reach4

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Given the long run lengths, what's the most efficient setup in this scenario, which will prevent pressure drops while running multiple fixtures AND get hot water there the quickest?
Not relocating the WH? Not doing recirculation system? Manifold for the hot using 3/8 PEX for delivery to lavatories. 1/2 inch for the tub. Dedicated shower could go either way depending on flow. Cold could either be branch plumbing for pipe efficiency or manifold for symmetry. I am not a pro. I have not tried to look at your fixture units.

Irrigation water gets tapped off before the whole house filter and the softener. If you have a well, there are other considerations.
 
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Unfortunately, hot water comes from the steam boiler, so only way to re-locate HW would be to install new stand alone heater. I had considered it, and was thinking to run 3/4 lines to the other side of house and manifold from that location (close to all fixtures).

This would allow me to install HWH in the future and only 'waste' the excess HW PEX from the boiler vs all the materials on a home run setup from the boiler.

Re circulation is an option.
 

Reach4

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I had considered it, and was thinking to run 3/4 lines to the other side of house and manifold from that location (close to all fixtures).
Unless you had recirc, that would cause a long time to get hot water for hand washing. Room temperature hand washing is not a hardship IMO. A low flow shower would take a while to get up to temperature with a long 3/4 inch run in the path.

From an energy efficiency standpoint, I think a button-triggered recirc would be best. Button-triggered could be a higher GPM (maybe 4 or 5 gpm thru 1/2 PEX) recirc and the wait would not be long.
 

Jadnashua

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The pex industry has a design manual. It's available for free online. There's a maximum flow rate for ANY pipe in the recommendations. The higher the flow rate, the more pressure drop there is. By comparing the charts in the manuals, you can decide how much you can live with. I don't think a 3/4" line will cut it, but that will depend on how many of the fixtures you ever expect to run at once. But, the larger the line, the longer it will take to purge. If you're going to repipe the house, consider adding a dedicated return line, even if you don't install recirculation, it will be there in case you change your mind. The alternative is to use the cold line, but then, that line will become warm. How warm, depends on the system you choose.

Given 75', and the maximum velocity recommended (pex is, I think about 8fps, copper about 5 with hot water, but check to be sure), you can figure out the time it would take for any size you choose. I'm familiar with copper. 1/2" copper at 5fps equals 4gpm. You can figure the volume of the line to see, at any velocity, how long it would take to purge the line. You'd need the ID of the tubing; then, pi*r^2*length. FWIW, a gallon of water = 231cuin.
 
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