In Floor Heat: Manifold Pipe Sizing

[shooon]

About took hook up my system, just wondering about sizing.
I Have a 4 port manifold with 4x 140' (ish) runs of 1/2" pex. Single zone, using a tankless water heater with 3/4" inlet and outlet.

Is 3/4" copper good for supply and return manifold piping? Or should I go with 1" copper? Supply pipe will probably be around 8-10' in length and the return will be about 4'

 

[garagelogician]

I'm assuming the tankless heater has its own integrated pump? Do you happen to know the specs (GPM and head pressure)? Are you using straight water?

 

[joe--h]

In & out are 3/4", there's no gain using larger pipe and reducers.