Cold vs. Hot Supply Size

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by freemarmoset, Jun 19, 2006.

  1. freemarmoset

    freemarmoset New Member

    Messages:
    12
    As part of a bathroom remodel, I'm taking the opportunity to replace rusty old galvanized throughout the whole house with copper.

    I have 1" copper from the street to the meter in the house (about 30').
    From the meter it's about another 70' to the furthest fixture.
    The hot water heater is right smack in the middle of that.

    I was thinking of running 1" from the meter to the back of the house with 3/4" branch lines for the fixtures. First, does that sound approximately correct? I've looked at the fixture unit tables (I have 30 Fixture units total) and it seems like that's basically correct.

    One of the tables I read though considered the feed to the hot water heater a branch line though which would make it 3/4"? That doesn't seem intuitively correct to me though? Shouldn't the main hot supply line be the same size as the cold--so 1" into the hot water heater, and 1" out?

    Thanks,
    Joe
  2. That will work and would possibly be considered overkill to size 3/4" to the fixtures they serve. Commonly 3/4" from main to water heater and out, reducing down to 1/2" to the last 3 fixtures they serve.
  3. freemarmoset

    freemarmoset New Member

    Messages:
    12
    Thanks a bunch.
    One more question:
    Should the horizontal branch lines from my main be 3/4" and step down to 1/2" for the short vertical runs supplying the fixtures, or should I just run 1/2" off the main?
    I guess the reason I tend toward overkill is that I'm just so sick the horrible water pressure I've been getting with the old 3/4" galvanized everywhere.
    :)
  4. Terry

    Terry Administrator Staff Member

    Messages:
    15,136
    Location:
    Bothell, Washington
    I don't like to run more than 2 fixtures on a 1/2" line.

    So for a "full bath", tub, lav, toilet it would be
    cold 3/4", pull off one fixture and branch to 1/2"
    hot 1/2"

    On the cold side, you have toilets and hosebibs for watering.
    http://www.terrylove.com/watersize.htm

    A nice way to do it, is to run 1" to the tee off for the water heater.
    Which depending on the amount of bathrooms, will either be 3/4" or 1".
    Last edited: Jul 9, 2006
  5. freemarmoset

    freemarmoset New Member

    Messages:
    12
    Thanks Terry. Since I'm a kinda green at this, let me make sure I undersatand correctly. Not sure what you mean by "pull off one fixture"

    So for cold I would t- off 3/4 at the water heater, then from that 3/4 in line for example, I'd t-off of twice...steppin down to 1/2" half in for the toilet, then say another 1/2" branch to the lav and the tub?

    Sorry, I'm still learning. The forum is a great place for it though. Thanks.
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,136
    Location:
    Bothell, Washington
    That's right.

    You want to make sure that if the toilet is flushed, it doesn't affect the person in the shower.
  7. speedball1

    speedball1 Retired plumber

    Messages:
    43
    Location:
    Sarasota Fl.
    In my area,(The Tampa Bay Area) We run 3/4" PVC from the meter to the house and 3/4' hot and cold mains. Code allows us to pick up three fixtures off a 1/2" branch but I like Terrys idea of a dedicated 1/2" line off the 3/4"main to pick up the toilet. No skalds there if you're in the shower and someone flushes the john. good luck, Tom
Similar Threads: Cold Supply
Forum Title Date
Plumbing Forum, Professional & DIY Advice Cold supply from 1" and hot from 3/4" to feed a large spa shower? May 5, 2014
Plumbing Forum, Professional & DIY Advice Cold Water Supply reduced to 3/4" before water heater... Sep 1, 2011
Plumbing Forum, Professional & DIY Advice Hot Water Coming from Cold Water Supply Dec 12, 2008
Plumbing Forum, Professional & DIY Advice How to move cold water supply 2 inches? Sep 15, 2007
Plumbing Forum, Professional & DIY Advice cold water feeding into hot water supply May 13, 2007

Share This Page