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