Is there any benefit to upsizing to 3/4" pipe off a 1/2" main supply?

Question

I have a half inch main supply coming from the street (house built in 1954). Is there any benefit if I run 3/4 PEX from the water meter to the various feeds and then branch off 1/2" PEX to the faucets? Does it increase the flow or will it reduce it? will it improve pressure?

Answer 1

Flow resistance, like electrical resistance, increases with conductor length. If you are going a long way (say, over 50 meters) you will get better flow by running a larger pipe. The volume is a non-issue - (static) pressure won't go down even if you install one of those giant green gas storage containers in the yard.

In no case will you get more flow than what the incoming pipe can provide--larger pipes just mean you will not lose part of this flow to resistance.

In a standard house you don't have enough piping (or demand) to make a difference.

Answer 2

Running 3/4" piping from the 1/2" feed will slightly decrease the pressure loss, meaning you'll get more pressure at your fixtures, but the difference will probably be very small. Most of the pressure loss will have already occurred in the 1/2" line before it reaches your house.

So, it will help some, but how much will depend on how long the run is compared to how long that 1/2" service connection is.

Answer 3

Pex and copper have differing inside diameters. Copper has the larger opening. As to 1/2 copper to 3/4 pex I dont know for sure.

This said I would not run my hot lines at the larger size as the pipe holds more water and will waste more water waiting for hot or sitting in the pipes cooling.

If you can insulate both hot and cold pipes... its a minor cost that will pay for it self soon.

Answer 4

You can have a 2 foot diameter pipe and not lose pressure! As a matter of fact you would be greatly extending your pressure tank capacity greatly. A larger pipe has less surface per volume of water. Going to a larger size would greatly reduce friction and help keep pressure. A half horsepower pump could push water across the United States if not for the friction of the water against the wall of the pipe. Push but not pull

Answer 5

It is true that 3/4 supplies more water and lowers pressure. When faced with this kind of question--resize to the ridiculous (you'll pass many tests with this trick too).

So if you have a 42 foot diameter pipe coming from the river to your house, what will the pressure be? 1 pound per square foot, perhaps? And almost zero resistance, and volume like crazy. Now pretend it is a natural hot water spring you're feeding from. You'll be waiting hours for all the non-moving water that has cooled in the pipe to move through your showerhead while the natural hot water spring refills the 42 foot pipe with fresh HOT water, eventually making its way to your shower.

The answer in short about your original question is, yes, change your mainline, but not to 3/4, instead to 1 inch PEX, this will greatly help flow, and will stop those annoying pressure drops when someone flushes a toilet while you're in the shower. MAKE SURE your hot water supply to the shower is 1/2" and insulated! There is a really good you tube video about this from one of the U.S. plumbing associations: search plumbing layout in you tube, and then look for a bunch of letters such as AAPPA or some such abbreviation as the uploader.

Answer 6

I was faced with this same question 20 yrs ago when proving to a Toto rep & former plumber on-site that despite satisfying all their specs and supplying the toilet with a 1/2” supply line, their very expensive toilet relatively new to the market failed the flush test and consistently required a 2nd flush. He came onsite to investigate & measured my mainline water pressure at 60 Psi well above the minimum psi requirements, then measured the water flow rate @ 6 gallons/min which met spec for the flow test using the garden hose just outside the bathroom. Finally, he thoroughly checked out the toilet & found no defects. At this point it dawned on him that there was a flow rate issue & all the psi in the world wasn't gonna provide the volume needed by the toilet to carry out the effective flush as intended by its designers. Flow rate- the missing link- at least as far as this toilet goes, & the one spec barely mentioned in fine print as an afterthought suggesting a flow rate of 6 gallons/min might work as an alternative if low psi, but not required. Stumped but determined & perhaps a little concerned, he then inspected the ½” supply to the toilet which was ½” blue pex which I used in my radiant floors. At a time when pex was not commonplace, and certainly not considered in the install manual I held up a piece of ½” pex next to 1/2” copper and pvc comparing the impressively narrower I.D. of pex, while informing him as well that the garden hose was plumbed using pvc from the same meter and the pex supplying the toilet was a relatively long run from its 1” pex mainline. He reluctantly concluded that the resistance from the longer run of pex to toilet from a pex mainline coupled with especially the narrower I.D. throttled the flow enough to affect the toilet’s performance. I was upset but was offered a gift of appeasement and noticed that future manuals mentioned flow rate requirements with more emphasis. I must say, I love pex but please don’t deny its shortcomings by stating there’s minuscule differences compared to copper.

Answer 7

There is no use in ever installing any plumbing that is bigger than your main supply line. At best you will have no issues. Worst case scenario is you will lose some pressure based on the increase in volume.

If you want to increase pressure you need to first increase the main supply line. If there is no chance of that happening then decrease as many things as you can to 1/4" (toilets, faucets).