3/4" or 1/2"???

edstengel · Dec 21, 2013

We are going to be plumbing a new store and some people have told me to use 3/4" instead of 1/2", and others have said that it does not make a difference, so here are 2 scenarios:

Static pressure = 50 psi
Service Dia. = 1"
Straight Length Of Pipe = 100 ft.
At End Of Pipe = Standard Faucet with Restrictions, connected to the supply line with 1/2"

What would be the qty. difference, if any, if I were to use 1/2" or 3/4" pipe to connect the 1" main to the faucet?

speedbump · Dec 21, 2013

Are you only feeding one faucet with the 1/2"? What kind of pipe are you using? PVC, CPVC, Poly or Pex? How many gallons per minute will this faucet use?

Caduceus · Dec 21, 2013

No toilets or mop sinks? No other appliances requiring water?
If the job is being inspected, you should look into what minimums may be required.
Plumbing inspectors in my area frown upon, but can not fail, a building with smaller than 3/4" trunk lines on commercial properties if the fixture demand doesn't warrant 3/4".
The idea is that any future additions to the building's fixtures could require more volume and additional work may create a financial burden on the owner. Inspectors realize that when more money is involved, owners are inclined to hire unlicensed contractors, cut corners and skip inspections that could possibly result in unsafe plumbing conditions.
Sounds like a round-about way of getting to the point, but it's all true and saves a lot of headaches for the owners.
I'm curious what type of store, in what area, would not have bathrooms or other minimum commercial requirements?

edstengel · Dec 21, 2013

Thanks for the replies. The system has much more than one faucet. All that I trying to establish, is, if you have 2 identical systems,and one uses 1/2" and the other one uses 3/4", with 1/2" supplies close to the taps, what is the relative difference (not exact numbers), between the 2 systems?

edstengel · Dec 22, 2013

Any thoughts speedbump or Caduceus? Should I get more, less or the same amount of water out of the tap if I use 3/4" lines or 1/2" lines? Thanks!

Caduceus · Dec 22, 2013

The difference is overall demand and the ability to keep up with it.
A 3/4" system will provide more volume to fulfill the needs of more than one fixture at a time.
This really depends on what the water supply is for as a whole, so that's a very important factor that is used by plumbers when sizing pipes.
Some people experience "pressure drops" when more fixtures are used at the same time. The drops typically are "volume drops" and are not associated with pressure. The end fixtures may have 1/2" connections, but if you use several 1/2" connections at once your demand will exceed your supply.
I have seen buildings with 1/2" trunk lines that have several toilets, sinks, janitors sinks, etc. and complain about pressure, boost the pressure up and then create more problems by damaging internal parts and solenoids.
3/4" would be my advice, but without knowing everything on the plumbing system your NEED may actually be more. There's a reason the service is 1" coming into the building as is required by code in Pittsburgh for commercial buildings.