On Tuesday, March 10, 2015 at 5:30:59 AM UTC-4, Gz wrote:
dpb wrote:
On 03/09/2015 2:53 AM, gregz wrote:
wrote:
I got a bathroom. I'm adding a second downstairs right below. ...
...
Run from hot water tank 20-25 feet, and cold tap. Still going to use the
1/2 feed from regulator and hot water tank.
...

I think you'll be sorely dissatisfied by the result if there's any
possibility whatsoever the two are being used together. That line needs to go to 3/4"...

--

Second full bathroom. The use of both would be very occasional. I'll have
to think about this a while and look things over. Things do slow down when
any two things are being operated. The house I grew up in didn't have any
fancy piping. I never really noticed a huge problem. The regulator might be
a factor too. I know air compressors regulators limit flow if undersized.

Greg

If you have 1/2" pipe serving the whole house, I'd bet that the
regulator isn't the limiting factor. I've never seen one with 1/2"
fittings and they typically size the fittings to accomodate the
capacity of the device. Around here, typically you have 1" pipe
coming in from the street, 3/4" pipe serving major/multiple points
of use in the house, 1/2" branch offs for half baths, kitchen,
laundry room, etc.

It seemed there was agreement here that if you do have 1/2" going
everywhere, then the safest option is to replace it with 3/4"
leaving the regulator, then one branch off to the new bath with either
1/2 or 3/4 and the other branch gets connected to the existing
rest of the house. If the rest of the house heads over towards the
new bath anyway, then just replace that section with 3/4". That gives
you 3/4" most of the way to the new bath and leaves the rest of the
house mostly better off too.