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Hot Tub

Bill_4 Member Posts: 16
A customer has a hot tub with a heat exchanger which ties into the boiler,the exchanger has 3/4' male threads,it would be alot easier to run 1/2" lines, what do you think?


  • Al Letellier
    Al Letellier Member Posts: 781
    hot tub

    It goes to heat transfer more than cost. Easier is usually cheaper too. Get the info for the heat exchanger and size accordingly. You could waste a lot of energy if the smaller piping doesn't transfer the heat properly, not to mention the time spent if you have to go back and re-pipe on your nickel!!!!

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  • It might work...

    it all depends on what the actual load of the hot tub is. If it's less than say 15,000 btuH, then 1/2" would probably carry it provided you have 180 degree water available.

    However, it is my experience that heat exchangers usually require a 2:1 source to demand flow ratio in order to work efficiently. In other words, if the HT has a load factor of 15K btuH, which would equal 1.5 GPM, then you'll need 3 GPM of 180 degree water flowing through the heat exchanger in order to deliver the goods. AN dyou probably could push 3 GPM through a 1/2" line, although it would be moving at 4 feet per second and would have a pressure drop of about 20 feet of head per 100 foot of pipe. Provided that you can meet all these parameters, then go for it. If not, consider upsizing, which will allow for more room for error and pick up after refill.

    Nothing worse than jonesing for a good soak and not being able to do it cause the tub ain't hot yet...

    How about using 5/8" Pex-Al-Pex?

  • sootmonkey
    sootmonkey Member Posts: 158

    You say that 1/2 inch copper has 20 feet of head loss at that flow rate. Would 20 feet of copper have 4 feet of head loss at the same flow rate? Soot.
  • I said...

    20 feet per 100 foot of pipe length, so in the case of 20 actual feet of equivilent pipe length, then yes, 4 foot of resistance at 3 GPM would be correct.

    You have to remember to add in the fittings equivilants also. An elbow = 3', a 45 = 1.5 ' etc.

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