Copper to Pex - infloor heating question
 

I am looking to install Pex with the fin plates under the plywood sub-floor in my bathroom to create in floor heating(I have access underneath - 2 x 10" floor joists). My plan is to connect to the existing 3/4" copper hot water baseboard line, loop the Pex between the joists, and then re-connect to the baseboard to continue the loop of the zone. My question is, do I need to use 1" Pex so I do not have issues with the water flow rate created by the hot-water furnace? Or can I use 3/4" or even 1/2". Thanks.