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Thread: Connecting water tank to 1" trunk

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    DIY Senior Member DavidTu's Avatar
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    Default Connecting water tank to 1" trunk

    According to our calcs based on hwsfu of 30 at water heater and given 80psi and 100' max dev length we should have a 1" main hot water trunk. The 80 gal tank we have has 3/4" connectors on it (or at least the flex lines are 3/4"). Can these be changed to 1" or can we get a tank with 1" connectors? If not do the 3/4" connectors not create a bottleneck and/or make the 1" trunk ineffective?

    The 1" trunk would be very short around 10' run connecting to two 3/4" branches on one end and a third 3/4" branch on the other end.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If the restriction is short in length, it won't make much difference - it will act more like a venturi - the liquid will speed up through the restriction to provide about the same volume. When the length of the restriction grows in length, the total friction increases, and you can no longer have the same volume - it will slow down, and that prevents the flow that a larger pipe could have. Some places require flex connectors (earthquake country), and some places prohibit them. You can probably find larger supplies in flex, if you need, or if allowed, hard pipe it with 1", and reduce right at the WH.
    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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    The diptube is 5/8" on a 3/4 heater. Just thought I'd throw that out there.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Many of the 75 gallon gas water heaters come with 1" nipples.
    You can also get 1" flex connectors.

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    DIY Senior Member DavidTu's Avatar
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    Quote Originally Posted by jadnashua View Post
    If the restriction is short in length, it won't make much difference.
    How short is short then? Right now I am contemplating running 1" PEX about 2ft in each direction to and from the water heater and keeping the existing nipples and flex lines (3/4")... I am hoping the 1" PEX from the water heater will act like a manifold from which I will tee-off three 3/4" lines running to various areas in the house. Is that worth doing or should I just leave it all 3/4" and skip the 1" altogether to/from the water heater?

    Also, on the 1" PEX cold line, does it matter if the water heater is the first of four tee-offs versus being last after the other three 3/4" lines going to those same various areas of the house?

    Regarding the nipples on the water heater... Terry says these can be 1" on 75 gal heaters... is that something that can be swapped out on an existing (80 gal) heater too? Or are we stuck with 3/4" if thats the way it was built?

    Thanks!

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    Quote Originally Posted by DavidTu View Post
    How short is short then? Right now I am contemplating running 1" PEX about 2ft in each direction to and from the water heater and keeping the existing nipples and flex lines (3/4")... I am hoping the 1" PEX from the water heater will act like a manifold from which I will tee-off three 3/4" lines running to various areas in the house. Is that worth doing or should I just leave it all 3/4" and skip the 1" altogether to/from the water heater?

    Also, on the 1" PEX cold line, does it matter if the water heater is the first of four tee-offs versus being last after the other three 3/4" lines going to those same various areas of the house?

    Regarding the nipples on the water heater... Terry says these can be 1" on 75 gal heaters... is that something that can be swapped out on an existing (80 gal) heater too? Or are we stuck with 3/4" if thats the way it was built?

    Thanks!
    I would bring all the 3/4 hot pipes to the water heater and build a small manifold out of copper to connect them to out of 1" and use the least amount of 1" pipe I could. Then buy me a suitable water heater with 1" inlets and outlet. OR Use two smaller heaters with 3/4 inlets and outlets and bull head a 3/4 x 3/4 x 1" copper tee. and pipe them in parallel with a bypass valve incase one went bad.......

    Thats just me.

    if you built the manifold outside the wall and brought all the 3/4 pipes to connect outside the wall and added a recirc. 1/2" line to the master bath you could add a circ pump easily to your bath and put it on a timer that matches your schedule. No waiting for hot water in the master!
    Last edited by Hackney plumbing; 02-07-2012 at 08:22 PM.

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    Two Rinnai 9.4 gpm units will run about 8 gpm at a 90 degree rise. Thats taking 50 degree water and making it 140 degrees.

    A 105 degree shower would be running 61% hot water. Lets say you want to run 2.5 gpm showerheads. Thats about 1.5 gpm of hot water per shower head.

    Those two tankless would allow you to run 5.3 showers at the same time.....forever.

    Fill the jaccuzi tub....forever.

    Two units would cost you 2,000.00

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