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3/8 lines run for pluming save water

ringshank's picture

I've been debating the issue with the local plumber about the saving water and energy ability by using 3/8 in plumbing ,run trunk style from a 1 in main line .. Over the life of the house this may save thousands of dollars in heating and water cost ... This would be fine to do right... This guy wants to run 3/4 close to the outlet then branch down to a 1/2 ... You would have to wait forever to get hot water up to the shower head .. As 3/4 pipe hold twice as much water as 3/8 .... Please let this debate end ... Who's right here 

Okay then, you lose. 3/8" (post #207438, reply #1 of 8)

Okay then, you lose. 3/8" tubing won't give you but about 4 gallons a minute which is not enough for most fixtures to work properly. You'll also lose more water pressure due to increased friction in small tubes and the increased speed of the water will make the tubes noisy.. The branch lines should be one size smaller than your main which in your case is 3/4". Your branches should be 1/2" until you get to the fixture where they can reduce to 3/8." In all probability your code will require 1/2" branch lines anyway.

Florida Licensed Building Contractor, 40 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.

Are you thinking of using a (post #207438, reply #2 of 8)

Are you thinking of using a manifold system? If so, 3/8 lines can indeed be used very successfully for most of the fixtures.

I know of literally thousands of houses where this has been done for decades, with no homeowner complaints regarding water delivery.

"3/4 pipe hold twice as much (post #207438, reply #3 of 8)

"3/4 pipe hold twice as much water as 3/8"

Actually, it's 4 times as much.

I wouldn't want to take a chance on the loss of that much volume. No way would I go less than 1/2"

 

 

Neither of you is right -- (post #207438, reply #4 of 8)

Neither of you is right -- 3/4" pipe actually holds 4 times as much water as 3/8" pipe.

The traditioinal approach is to run 3/4" copper pipe to a point near the bathroom and then split into 1/2" copper pipe for individual fixtures.

There are advocates for "home-running" 1/2" or 3/8" plastic pipe, feeding only 1 or 2 fixtures (in the same room) each.  This gets hot water there sooner, and thus can save water/energy if there's a significant distance to cover and you're the type who always waits for the water to get hot before you wash your hands.

There is the problem, though, that 3/8" for that distance is beginning to negatively impact flow.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

So Some of this makes , I (post #207438, reply #5 of 8)

So Some of this makes , I would run a branch type system with 3/4 main ... 3/8 to each fixture.. Most distance for the 3/8 would be 20 feet ....I'm not talking 60 feet here ..... Any way the tube coming out of the faucet  is only a 1/4 in! Not sure . But simple solutions can save money ?

By running a 3/4" "main" you (post #207438, reply #6 of 8)

By running a 3/4" "main" you lose much of the advantage of the 3/8" pipe.  This is why "home running" is advocated -- the individual 3/8" hot water pipe is run all the way back to a manifold near the water heater.  (Cold, OTOH, can be handled in a conventional fashion.)


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Besides the 1/4" inlet to the (post #207438, reply #7 of 8)

Besides the 1/4" inlet to the faucet, it's also a fact that modern plumbing fixtures are all restricted to deliver less water--faucets for sinks and showers are limited to less than 3 gallons per minute.

A 3/8" pex line can deliver 6 gpm at 50 psi over a distance of 40 feet.. (Using Hazen Williams formula.)

You can do your own experiments on this by just running water thru your proposed length of 3/8 tubing and timing how long it takes to fill a 5-gallon bucket.

3/8 pex limit (post #207438, reply #8 of 8)

rdesigns wrote:

A 3/8" pex line can deliver 6 gpm at 50 psi over a distance of 40 feet.. (Using Hazen Williams formula.)

If I recall correctly, IPC limits water velocity based on pipe material and diameter, and I think the limit is somewhere around 8ft/s which limits 3/8" pex delivery below that 6 gpm figure.  The velocity limit is supposed to prevent pitting, which can occur at fittings, perhaps at tight bends in the pex itself.