2 hot lines to one fixture with check valve

[JeffT]

I have this idea to solve the dilemma of hot water delay vs. volume.

I have a bathroom (sink, toilet, bath/shower) a long way from the water heater. I'll run 3/4" pex for the cold. I'm thinking of running two 1/2" hot lines; one will normally feed the sink, the other will only feed the shower/tub.

But what if I allow the shower/tub to draw from the sink hot line as well? I'll put a check valve between the hot lines that keeps the sink from drawing from the shower/tub feed.

Won't that give me fastest possible hot water for the sink and high hot water volume for showering and filling the tub?

Please debunk this idea before I try it!
Thanks!

 

[Terry]

You can run a tub and a lav on a single 1/2" line. That is normally what I do, or you can run the two lines for that. They also make 3/8" PEX is you want to unload the line quicker. Skip the check valve. It's all under pressure anyway.
3/4" for the cold is needed as you are also adding the toilet.