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Pipe size

StangobStangob Member Posts: 24
Hello all. I have come back to a great resource in hopes of getting great advice once again.
This weekend I had a leak. I went to the shut of valve no luck. Went to another valve no luck. Long story short it looks like previous owner just cut and tapped pipes at random.
I would like to cut out this spaghetti like set up ant stream line it. My idea is home run to water heater and then to manifold of sort (shut of valves to each room). I have 5/8 line coming into house. My question is can I use 3/4 from meter till fixtures or stick with 1/2 inch? Also can I run pipe on bottom 1/3 of wall in basement (pipe would be protected from accidental penetration) instead of overhead in joist cavities?
Thanks in advance for the advice.


  • JUGHNEJUGHNE Member Posts: 6,966
    Where did you get the 5/8" number from?
    Pretty typical is 3/4" (7/8" OD) service line coming into the house.
    Some water meters are called 5/8" (internally) but have 3/4" connections.
  • ZmanZman Member Posts: 5,869
    The bigger 3/4" pipe has no downside. The reduced velocity should reduce potential for pin hole leaks. Are you talking about plumbing in an exterior wall? Is is below grade? What climate?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • StangobStangob Member Posts: 24
    I got the 5/8 from my water bill. Will double check when I get home about actual size entering house. I do know that from my side of the meter it's all 1/2 inch. I live on Long Island NY. The space is in a basement. Unfortunately the basement ceiling is finished. So I would like to take the easier route if possible and go along the wall where my return for boiler condensate runs. The house is set up as the water comes in runs about 75 feet (25 to back wall then 90 degree turn)to hot water tank then runs back 75 feet and then up to fixtures. All plumbing fixtures are located on same back corner of house. 1st floor kitchen and 1/2bath next to each other and then 2nd floor full bath.
  • Jamie HallJamie Hall Member Posts: 12,947
    You could use half inch. However, for runs of that length -- particularly to the water heater -- I'd rather see you use three quarter. For the same flow, you'd lose only half as much pressure that way. It's no harder to work with, and the fittings are readily available. You can transition to half inch with a reducer -- straight, T or elbow -- where you need to.

    And no, there's no harm to running on the wall of the basement. Makes life a lot easier...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • JUGHNEJUGHNE Member Posts: 6,966
    We have a fairly low 35 PSI here. So our rule of thumb was to have no more than 2 connections on a single 1/2" pipe.
    You may have quite high water pressure there making all the difference.
  • StangobStangob Member Posts: 24
    That's what I was thinking. 3/4 from meter and transition to 1/2 inch at fixtures. I can certainly check the pressure. What range should I be looking at to use 3/4 pipe? Thanks again guys for all the help.
  • Jamie HallJamie Hall Member Posts: 12,947
    The only conceivable reason I can see to using half inch for anything except the fixture feeds is the very slight additional cost of materials for the larger size.

    If your inlet pressure is anything below 60 psi, use the three quarters and don't cheap it out.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • KC_JonesKC_Jones Member Posts: 4,411
    From personal experience I would say do the 3/4" with 1/2" to fixtures and don't worry about the calculations or pressure. I did this in my own home years ago after a previous person had plumbed everything in 1/2" CPVC. I used copper 3/4" throughout house with 1/2" branches to the fixtures. I went from not being able to do anything while people showered to being able to flush toilets and wash dishes etc. while people showered with no loss of pressure or flow. The difference was dramatic. Also will add I have extremely good water pressure and it was still a big problem with the (IMHO) under sized pipes.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • JUGHNEJUGHNE Member Posts: 6,966
    There are at least 4 configurations of 3/4" tees. By using the reducing tees you can eliminate extra reducing couplings. You could see the varieties at the store.
  • StangobStangob Member Posts: 24
    Thanks for the advice guys. Looks like the plan is 3/4 pipe and reduce at fixtures. Looks like weekend just got busy. Lol
  • RomanGK_26986764589RomanGK_26986764589 Member Posts: 221
    @KC_Jones I had the same issue when I bought my house, All of the piping was done in 1/2". I converted to 3/4" with 1/2" to the fixtures. Much better water flow now. :) However, I see folks on the internet often recommend piping 1/2" for hot water but do not specify exact reasons. Is it to save on hot water? Or are there any other reasons for doing so?
  • rick in Alaskarick in Alaska Member Posts: 1,086
    1/2 inch pipe has less volume, so hot water can get to the fixture faster, and with less chance of cooling off because of the lesser amount of surface area. However, it also has more of a restriction in it, so you would have to take that in account if it had very far to travel. You would have to get out the charts and calculate out flow rates and temperature drops to know for sure how far you could go with 1/2 inch before it starts to become a problem.
  • JackJack Member Posts: 1,044
    If you look at the cross sectional area of 1/2, 3/4 & 1" pipe it is .19, .44 and .78 respectively. That equates to volume that on the cold side makes not a lot of difference, but on the hot side...delay.
  • hot_rodhot_rod Member Posts: 13,474
    The pressure you have to work with makes a big difference. Most homes regulate down to 45 psi if the street pressure is higher than that. Homes with low pressure might use a Grundfos Scala pressure booster pump to get to 45-50 psi.

    You might look into the Viega Manabloc system. Originally developer to allow piping with PB tube and not have any fittings buried in walls. It is a hand way to homerun and end up with a nice manifold and valves for every fixture.

    In some cases the Manabloc "formula" allowed 3/8 tube to fixtures like low flow laws and dishwashers. The other goal was fast hot water without the n need to recirculate. 1/2 pex holds about 1 gallon per 100', so it, and 3/8" flush within seconds to deliver hot water.

    Rarely was any branch over 1/2" save for roman tub fillers, as I recall up to 70' runs max. from the manifold.

    I see Viega FoastaPex now has NSF approval for domestic water, that would make a nice tube for H&C water piping in red and blue color, if it adapts to the block.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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