I'm switching my trunk and branch plumbing system.over to manifolds with 3/4 inlet and 1/2 outlets.

Would it be better to Tee the line off to the hot water heater before the cold water manifold (and thus using a 3/4 input line to hot water heater)? Or better to use one of the cold waters 1/2 outlets to feed into hot water heater? If I use the 1/2 inlet to hot water heater, can I still output with 3/4 or would I have to use a 1/2 line coming out of hot water heater into hot water manifold (with appropriate sized adapters)?

2 Answers 2


On manifold systems, I have never seen the hot water taken after the cold manifold. It has always been a tee off the main line. If you are running dedicated lines to each fixture in all locations, 1/2" lines will work in all cases. If you are going to branch off to other fixtures using one line to do multiple fixtures, say one line to do a bath, another to do the kitchen and another to do a hall bath, you need to start with 3/4" lines from the manifold, then reduce to 1/2" after a few fixtures have been fed.

  • I would want a full size supply line to the water heater also.+
    – Ed Beal
    Commented Feb 2, 2018 at 17:32

In my last 2 houses, all the main water lines were 3/4" with reducing tees 3/4"X3/4"X1/2" or 3/4"X1/2"X3/4" used to service each device. No 1/2" tees were allowed in the plumbing.There has never been a scalding/freezing complaint in either house and no loss of flow when another fixture was used. All the water lines were type "L" copper. I do not like the new way houses are being plumbed in my area using a hot and cold manifold made of some kind of plastic material with 1/2" feed lines to each device. (call me old school). I use a return pump to insure almost instant hot water at every sink, bath or shower. Works great, saves money,and makes everyone happy; you know the cliche, "happy wife etc. This may not be the answer you are looking for but it is my tried and tested recommendation. hope this helps

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