Re: Hot water supply sizing
Posted by Hube on February 17, 2004 at 19:11:51:
In response to Re: Hot water supply sizing
: Run the 1/2", here's why. The cold water held in a 20 ft length of pipe is considerably more in a 3/4" than a 1/2" diameter pipe. There are formulas that I don't have or remember that would compute volume exactly, but the one I do remember should illustrate closely enough what I mean. The area of a circle is equal to the square of the diameter divided by .7854. It figures out to about .08 sq inches to .72 sq inches! That 9 times as much cold water in the 3/4" line that has to be purged before you get hot water. When I replumbed, I though it would be great to run 3/4" pipes for the main supply lines. Well, it's fine on the cold water side, but when I went to use the hot water in the bathroom some 30 feet of pipe away, it took forever to get hot water and many gallons of wasted water. I changed back to 1/2", and now it takes about 12 to 15 seconds, and the 1/2" flow volume is just fine for a few fixtures.

Gary; Check your math. A 3/4" pipe has approx 3 times the volume of a 1/2" pipe.. (not 9 times.) Hube

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