We are in the process of remodeling and I am doing the plumbing.
To make this really simple draw a T on a piece of paper. The vertical part of the T connects to the hot water heater and is 3/4" copper. The left side of the T is 3/4" copper that runs to the kitchen, a secondary bathroom and the laundry room. This side of the supply line is 3/4" to the kitchen where it is reduced to 1/2". The 1/2" line feeds the sink, shower and laundry.
The right side of the T was immediately reduced to 1/2" and that feed the main bathroom (shower and sink).
We are in the process of adding a new basement bathroom directly below the main bathroom and I was concerned that a 1/2" supply line would not be sufficient for both bathrooms. So I upgraded the 1/2" supply line to 3/4" and then broke off with 1/2" T fittings for the main shower and faucet and then again to the new shower and faucet.
So basically I have a straight 3/4" supply line from the hot water heater that has 4 T fittings (each 3/4" to 1/2") for each faucet and shower. I hope that makes sense.
The problem is that since doing this our main bath/shower is only getting warm water even with no other fixture on. Initially it is hot but then it drops down to luck warm and we can't seem to get it any hotter.
So the question is should I have only upgraded the supply line to 3/4" to the first fixture and then continued with 1/2" to the other fixtures?
Sorry for the long description... any help would be greatly appreciated.