1/2 inch PEX to tub. no volume

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Plumber69

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Pressure in this town is as low as 40 psi, high as 60 psi. 50 psi or below I can't seem to get enough volume to tubs running half inch PEX. Branched of a 3/4 line. Will I get more volume running 3/4 PEX right to the tub. Even though I'm adapting to a half inch tub rough in
 
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Jadnashua

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SHort answer - YES. The id of 1/2" pex is closer to 3/8" copper. THe ID of 3/4" pex is larger than 1/2" copper. If you use crimp connections, the volume throughput is slightly less than if you use the expansion system of fittings and tubing. Restrictions mean friction, which means less volume.
 

Jadnashua

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Fluid dynamics functions such that in a short distance restriction, the fluid speed increases through the restriction, then returns to 'normal'. This is the venturi effect. A long section of smaller diameter does not return to the normal flow rate...it just creates friction, and reduces the max volume available.
venturi3.gif
 

Reach4

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1/2 inch will get hot water there a little sooner, but that is not so important with a tub as it would be for a lav.

Most people use more hot than cold in a bath or shower. You might consider just bumping the hot line up to 3/4.
 

Jadnashua

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This is a good handbook on water piping. It's about copper, but the concept is also valid for any tubing material...the flow rates will be lower because of the ID, but if pex is installed reasonably (i.e., not like rigid copper with lots of fittings), the lack of fittings can help. http://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf
 

Magneto

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Jadnashua is 100 percent correct. Use less fitting and you should be fine. Make sure everything is spaced properly and maybe you might want to invest in a pressure pump.
 
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