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My 2.5 bathroom home was built in 2016. The water main coming in from the city is 1-inch PEX pipe. City pressure is assumed to be very adequate. Before the pressure regulator, the pipe reduces to 3/4 inch. So all of the pipes in the house are 3/4 or 1/2 inch. The house has a basement, and the basement is unfinished. So access to the pipes is not at all an issue. Should I increase the pipe size by swapping out the current pipe with a 1 inch pipe to the utility room (a 50-60 ft run to where the hot water branches off from the cold)? I am going to add a water softener (the water softener was built for 1-inch pipe), and so now is a good time to address this if it's a good idea to address it.

Here is what I currently have:

  • 3 toilets
  • 1 washing machine
  • 1 dishwasher
  • 1 fridge with ice maker
  • 5 bathroom sinks (2 of the bathrooms have 2 sinks each)
  • 1 kitchen sink
  • 2 hose bibs for gardening outside (rarely used since we have secondary water for watering the lawn with)
  • 1 shower (without tub)
  • 1 large tub (without shower) -- same bathroom as above shower
  • 1 tub/shower combo (a normal United States tub)

and in the immediate future I'm adding a water softener. In the long-term (when the basement is finished) I will definitely add these additional fixtures:

  • 1 tub/shower combo
  • 1 toilet
  • 1 bathroom sink

and desire to put a basement kitchen in as well (not sure on whether I will add a dishwasher).

We have two adults and 6 children currently living here. They aren't teens yet but that's not too far away. My water needs will be greater in the future. We may have additional adults living in the basement when it has been completed.

I talked with a plumber over the phone about it, he said not to worry about it, if it was his house he wouldn't worry about it. However I'm unclear on whether he was considering the future bathroom and kitchen which will be in the basement. He also did not know how many children I have :).

I worry because others in my neighborhood (same floor plan as my house) have the 1-inch pipe into the utility room. But my house does not.

  • Your largest water demands are the hose bibs and tub. If these have 3/4 supply's I wouldn't spend a bunch to increase the size. The toilets and sinks at max have 1/2" lines but after the valves the lines are usually 3/8". Your larger shower may have 3/4 if multiple heads but remember the shower and tub have both hot and cold going to them. The only reason to upsize would be if you have a drop in pressure with multiple faucets being used. – Ed Beal Sep 19 '16 at 17:44
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Comparing the pressure drop between 50' of 3/4" and 1" PEX...going up to 1" saves 1 psi at 5 GPM flow rate, and 5 psi at 9 GPM and 7 psi at 11 GPM (when you hit 10 feet per second in 3/4" PEX, a velocity which shouldn't be exceeded). In other words, you need to have pretty significant concurrent demands before the pressure drop in that pipe run becomes noticeable (or where pipe erosion from high velocity becomes a concern) - like filling two tubs or taking four showers at the exact same time, plus running a dishwasher or washing machine. It's possible that with so many kids that's actually a reasonable concern for you, but for the typical household there would be little benefit.

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Personally, I'd do the 1-inch to the hot / cold split, at least. I guess that might mean upgrading the PRV, if the PRV is a 3/4" PRV.

Standards evolve. Used to be pretty common to have 1/2" pipe for the whole system, which was abysmal, but abysmal was considered "normal."

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