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

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 5

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 6

It's extremely unlikely you have a 1/2" main.

Firstly, tripple-check that you actually have a 1/2" main. This was even unlikely in the 1940s, more than a decade before your house was built. Out of at least 50 people that told me they have 1/2" supply line, nobody was ever correct, even once. Please make 100% sure this is the case.

It's much more likely that someone reduced your water line to 1/2 right at, or close to the main, and you actually have a 3/4" or 1" main. In every case, this turned out to be the real case in my experience.

If you REALLY have a 1/2" main. You'll see a difference only if you increase your pressure with a pump AND you add a tank to provide the difference in pressure if you use more than 14gpm, just increasing the line size will matter, but it will matter close to zero.

You probably have a 3/4" line; what's the difference if you do?

The rest of this answer is for people that think they have a 1/2" line but if they remove their cabinets or dig deeper, they'll see they actually have 3/4" and aren't sure if it's worth it to use it, or don't know what the difference is...

Yes. It makes a BIG difference. Since most things only input 1/2" lines (except hot water heaters and manifolds), you should use a 3/4" line to your hot water heater and manifold, which will distribute the pressure evenly throughout your home. A 3/4" line to a manifold is like heaven... someone flushed while you shower? NO PROBLEM!

You will get about 70% more flow with pressure being equal (specifically, 24gpm in 3/4" at 50psi vs 14gpm in 1/2" at 50psi (50psi is pretty standard city pressure)). This will vary slightly in various pipe types, but it's roughly 70% more.

Your city will push about 50psi to your home in a 3/4" line, which is standard in the US, anyone not using this is wasting pleasure the city provides you, plain and simple. 40psi is considered low, and above 60psi will damage equipment like hot water heaters.

40-50psi in a shower is considered extremely comfortable and will spray dirt off your body and feel like a massage.

Lower than that and people start reporting being annoyed. A shower at 30psi sucks. A shower at 20psi is really annoying.

Just one appliance being used on a 1/2" line will dip your pressure below 30psi!

When you use water by turning on a faucet, that 50psi pressure goes down in the entire water circuit, down to near zero if you consume your max flow rate. I.e. if you consume 14gpm in a 1/2" line, the water will be at near zero pressure.

Most faucets will use 2-3gpm.

Showers use 2-5gpm per head, so a single 2 head shower uses nearly all pressure in a 1/2" line, but less than half of the pressure in a 3/4" line.

Low flow is 2.3gpm.

A toilet or appliance like a dishwasher or washer can consume 5 or more gpm for short periods. These, if on while you're showering, can reduce the pressure of your shower below 30psi. If they consume hot water, the hot line will drop to 30psi or lower, and the mixing valve will mix more cold in the line than you originally dialed in (when both were at the same pressure), resulting in you freezing your nipples off (a dishwasher alone can do this on a 1/2" line, but on a 3/4" line connecting to a manifold, you would not even notice z the pressure will only drop a few PSI).

Since a 3/4" line can delivery 70% more water, your pressure will go down 70% less when other stuff is running because the water you take out will be replaced 70% faster.

This is not only noticeable, it's NIGHT AND DAY DIFFERENT.

The best way to get the least pressure difference is to use a manifold right at the city inlet with 3/4" input.

Modern water heaters are also 3/4". Make sure you supply your home with a full flow 3/4" hot water line or you'll suffer for no reason the entire time you live there.

Water pressure is a solved problem. Just use the full 3/4" capacity... it's there for a reason. Your taxes pay for it. Take advantage of it!

NOTE: using a 3/4" line from the city, running it 20 feet and then reducing it to 1/2" does virtually NOTHING; you MUST distribute this 3/4" flow to at least 2 or more 1/2" lines to see a difference. This is what a manifold does. Make sure you connect it to a manifold or you will spend extra money for nothing!

Answer 7

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 8

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).