Hot Water Supply Sizing

[P-tank]

i'm looking to supply a 20 gal hw tank (laars endurance boiler) with 3/4" line for 2 floor 2 full bath unit. then i guess i'll run 3/4" line out too. but recently was wondering if i shouldn't go with 1/2" instead, thinking tap and shower might warm up quicker.

current connects to tank ar 1/2" but step up to 3/4" to enter the actual unit. i'm worried about adequate flow, etc. the hw part of this boiler has not been in use as of yet.

any thoughts and advice much appreciated

[Gary Swart]

I think you have a valid concern about the time it takes to purge cold water from 3/4" lines, especially to the furthest fixture. I think 1/2" would be quite adaquate.

[Terry]

Most plumbers are running at most 2 plumbing fixtures on a 1/2" line.

Tubs are rated at 4.0 fixture units, lavs at 1.0 for a combined total of 5.0
If you check the charts, you will see that 1/2" lines don't handle much more, maybe one more 1.0 lav.
Two bathroom groups, you should have 3/4" pipe.
http://terrylove.com/watersize.htm

http://www.iapmo.org/common/ROP2004/upc04rop/preprint/ch6.pdf

[P-tank]

ok, thanks, i see this is a debated topic. i think i'll probably go with 3/4".