I would like to supply my water heater with two 1/2" lines (one hot one cold)into one 3/4" then into the water heater. The reason for this is during the winter my hot water comes from a coil that runs through the boiler, in the summer it comes from an electric water heater. The problem is the "winter" hot water comes from 1/2" lines and the hot water flow is slow at the tub or shower. So during the winter I want have the so called free hot water run into the electric water heater along with another 1/2" of cold to keep the 3/4" supply line flow proper. My thinking here is it may help the electric heater to work less. I believe they don't make a copper "Y" so I would have to go with a "T" fitting with one 3/4 and two 1/2" ends. Providing both 1/2" lines have equal pressure would one line get an advantage or would the water be mixed equally regardless of which end they come in from? Is 1/2" okay or should I use reducers so they are 3/8" & 3/8" instead?