On a radiant heat system, is it better to put circulating pump before supply manifiold or after return manifold?

Pump away from boiler is standard practice BUT I always tell people to look at the manufactures instructions for the boiler being used.

There is no boiler. Heat source will be a water-to-water heat pump using well water as the source and the water in the floor tubing as its load.

Now more info comes out. You did not state your somewhat nonconventional heat source. In this case I do not believe it makes a difference where you put the pump as long as it is on the opposite side of where the expansion tank is located. Good luck with your project.

I purchase a four loop rifeng manifold and as I running the tube it looks like I will need two extra loops. My question is if I buy a two loop rifeng can I hook it to the four loop to make it a six loop?