:> :> Thanks Bob. I'm rubbing my chin on that one and trying to understand it.
:> :> You forgot the link!
:> :> Dan
:> Ah, thanks. The subject is:
:> "Pressure Loss of Water Due to Friction in Copper Tubes"
:> My intuition on this is that the friction component using copper tubing
:> (especially new) is going to be WAY less than my old rusty galvanized
:> 1/2". Add to that the fact that the cross section of the interior of
:> 3/4" pipe is 2.25 times that of 1/2" pipe, and you have MUCH better
:> water flow and pressure. That's intuitive, of course. The linked page
:> and it's table is based on engineering science.
:Your intuition is correct.......YEARS ago (1979) I was having the
:shower feeds in my 1930 house redone
:I was so fed up with low water pressure I was going to make the plumber
:replace my 59 year old 1/2 galv with 3/4" cooper feeding first floor
:shower & then onto the 2nd floor.
:I really water 3/4" copper the plumber talked me out of it....saying
:the "flow factor" of old copper tube is way better than new glav. I
:went with 1/2" copper.
Today I had a look at the old water main shutoff valve that they cut out
when they replaced the water main. On either side is galvanized pipe and
on one side I could see rust that reduced the 1/2" internal diameter by
at least a factor of 2. And that is just one spot. And the knobby rusty
obstruction was clearly doing more than restricting flow by reducing the
effective diameter. It was adding a tremendous amount of turbulence,
which would very significantly reduce the gpm delivered to various
sytems in my house. I'm contemplating replacing some of the interior
piping, but I really have no good reason to do so presently. My
pressures are good, at least partly because of the high pressure
delivered to the house. I should probably actually have a pressure
reduction valve where the main surfaces at the front of the house. A
Plumber told me they are $100 and I believe they only reduce the psi by
:Fast forward to 2007 & now I finally getting around to doing the rest
:of the house.
:I'm going to use PEX w/ a home run system. I'm torn about replacing
:the perfectly still good copper but I may as well since the walls will
:The 16' run to 1st floor shower & the 26' run to second floor
:Worst case with 125F hot water & 45F cold water (that's pretty cold)
:.....I'll need 1.5 gpm hot & .5 gpm cold to service a 2gpm shower
My requirements are different because I live alone. I envision selling
the house, so the buyer's requirements will be greater than mine.
Myself, I have an on demand WH, which has a remote and I keep the
temperature at the lowest, which is 100 degrees. When I take a shower, I
push that to 110 in the summer and 115 in winter. When it's chilly, 115
delivers a perfect shower using hot water only. I guess that even if
someone were to flush a toilet while I was taking a shower it wouldn't
much affect the water temperature.
If you have a lot of people in the house, measures like mine aren't
practical, obviously. You have constant hot water temperature and deal
:A run of 1/2" PEX 26' long will only drop ~1.8psi
:My house is fed with 1" copper (~50' to the street) another 25' of 1"
:PEX to the hot/cold split
:1" feeding the cold manifold & 1" feeding the hot manifold
:If I run the dishwasher (~2gpm) & two showers (2 gpm ea) I'll need
:~6gpm to the house & 5 gpm hot water
I don't have a dishwasher yet.
:The thing that causes problems is not only the pressure drop but the
:change in pressure drop as water demand increases or decreases. When
:you're taking a shower & you have the temp adjust you don't want
:significant increases or decreases in water pressure where you're using
:it....reduction is total pressure is annoying enough but when the hot
:or cold pressure changes alone...it can be more than annoying.
I'm amazed that my shower flow doesn't appear to drop much AT ALL, when
I flush the toilet now with my new water main installed.
:Unfortunately that table of copper tube pressure drops leaves a little
:to be desires wrt significant figures......only one in most of the
:anyway if you play around with the numbers you'll probably find that a
:3/4" line will supply most reasonable home usage without significant
:pressure drop.....unless you get the washer going, the dishwasher, two
:showers & a random toilet flushing.
:But hey, I'm just happy if I can take a shower & not be bothered by
:one or two other water usages.
That would be nice.