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Thread: Does 2+2 = 4?

  1. #1
    DIY Member RinconVTR's Avatar
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    Default Does 2+2 = 4?

    As far as venting goes, can the requirement for 4" PVC be run using TWO 2" pipes for the run between unit and the outside? Meaning I would have FOUR 2" pipes running inline with each other until termination on each end.

  2. #2
    In the trades Dana's Avatar
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    The cross sectional area of at 4" pipe is: (π x 2 x 2=) ~12.57"

    The cross sectional area of two 2" pipes is: 2 x (π x 1 x 1=) ~6.28"

    So it would take FOUR 2" pipes ( 2" + 2" + 2" + 2" = 4") to equal the same cross sectional area, which what counts as far venting goes (pretty much, more or less).

    Whether that would meet the letter of code or pass inspection is dubious at best though.

  3. #3
    DIY Member RinconVTR's Avatar
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    Quote Originally Posted by Dana View Post
    The cross sectional area of at 4" pipe is: (π x 2 x 2=) ~12.57"

    The cross sectional area of two 2" pipes is: 2 x (π x 1 x 1=) ~6.28"

    So it would take FOUR 2" pipes ( 2" + 2" + 2" + 2" = 4") to equal the same cross sectional area, which what counts as far venting goes (pretty much, more or less).


    Whether that would meet the letter of code or pass inspection is dubious at best though.
    Yes, I know the math (thanks for pointing out how horrible it compares!) but you also ended by hitting the true intent of my question. Code doesnt always equate to engineering, sometimes the rules, regs, and local codes make no sense to anyone.

    Whats really behind the question...well in my home the situation exsists to run at least 4 (may be I could do more but thats getting REALLY carried away) - 2" tubes veritcal, thru the middle of my home and out the roof VS routing 2 big 4" pipe to the outside, and on the side of the home, at a very visible location.

    I'm trying hard not call it quits on any type PVC vented water heater (I really want closed combustion) but I have to make a decision soon. My tank is 14 years old and my kids are begining to take daily showers.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    I would much rather side vent than go up through the roof...it might be easier to move some supply lines so those pvc lines go somewhere you can live with. WIth making a manifold on each end to split then recombine the pipes, you'd be adding a huge restriction and probably would exceed the max run length because of them (each turn equates to a fair length of straight pipe - it adds up quickly).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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