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sharp 05-04-2010 09:21 PM

water supply size
If I have a 3/4 pipe entering my house from the water supply, is there any benefit from using a 1" pipe to run the water supply throughout the house.
Also,this 1" will be cold water, does it matter that the hot water pipes are 3/4". The material L copper.


waterman1971 05-04-2010 09:35 PM

Reduced velocity could add to the life of the plumbing. Why is this even a consideration? Maybe on your washing machine or dishwasher? Just thought i'd chime in.

sharp 05-04-2010 09:44 PM

I'm in the middle of a major renovation and where I'm living now the shower loses water pressure whenever any other fixture is running. This is something I want to avoid. My house is 80 years old. It seems new construction comes with a 1" supply line coming into the house. I only have 3/4 coming in. Don't want to change that, but wanted to know if continuing from the supply 3/4 with a 1" if that would reduce the chances of losing water pressure in the second floor shower when the washing machine and diswasher are running.

waterman1971 05-04-2010 09:50 PM

The water pressure will not change regardless of the diameter of the piping supply line. The volume of water you can deliver, however, will increase as the diameter increases. Try measuring the flow rate at the new location vs. the old. If the difference is significant perhaps increased diameter could help. Maybe there is an obstruction somewhere, galvanized nipple or something?

The Engineer 05-05-2010 09:16 AM

There are two type of pressures in your system, the static pressure under no flow will remain the same no matter what diameter pipe your running, you'll only lose pressure to elevation because of the 2nd floor. Once you open a valve and start flowing water the pressure drops down to a "residual" pressure based on your flow, pipe size and friction loss. If your 1" pipe run is any significant distance, you will gain back some of the friction loss, but if your run is short, any gain in pressure will be mimimal. For example, if your 3/4" service is 100 feet long, and you run a 1" pipe after the meter only 25 feet, you won't gain much pressure. But if your 3/4" service pipe is 25' long, and you run a 1" pipe 100 feet after that, the friction loss gained will be more significant.

Yoyizit 05-05-2010 10:06 AM

(1/0.75)^2 = a factor of 1.8 larger in pipe capacity.

Try these guys for some numbers

The friction loss depends on the water velocity squared, and velocity depends on GPM and pipe size.

IMO the public water supply acts more like a 'pressure source' [constant pressure regardless of flow rate over a zero to 13 GPM range]
rather than acting like a 'flow source' [pressure adjusts to provide a constant flow].

Like Mr. 1971 said, what is your shower GPM, with and without other fixtures running? All you need to check this is a known capacity container and a watch. I'm sure it's less than 6 GPM in any case.

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