two 1/2" lines feeding one 3/4" supply line?
I am in the process of installing a new Manabloc pex manifold. I am doing home runs on each appliance in the kitchen, 2 bathrooms, utility room , and mud room, which are all centrally located near the utility room where the manifold is being installed.
The problem comes with a master bath that has a 3/4" supply going to it. All of the piping is not accessible (buried below sub floor from above, hidden above spray foam from below). Furthermore, it is a decent run to the master bath, 30' or so. So supplying hot water on a shower home run and then getting out of the shower and supplying hot water to the sink on a home run is a lot of waste, sending it over in one supply is preferable.
With all that being said my question is can I use 2 of the ports on the manifold to feed into one of the 3/4" supply lines for that bath? The math says that two 1/2" lines (.39 sq in) is just a tad smaller in volume than one 3/4" line (.44 sq in).
My concern is not the volume, rather it is the circuit looping back on itself. Maybe it's a non-issue due to equal pressure, or maybe there is some other possible problem with this setup that I don't know about. I wanted to get advice before I did it.