Can I use copper manifolds in radiant floor heating?

The problem your having I assume comes from the fact that stainless steel manifolds come equipped with air vents, air eliminators, gauges, shut-off valves, drain valves, etc. Just so you are aware all these items should be purchased separately, and you should do some more research to determine what components your system is missing.

Best option if you buy regular stainless steel pex manifolds. You will find its on the same website canarsee supply they have all what you need in one kit. Don't outsmart yourself

Yes you can use copper manifold for radiant heat but you get some headache with air in the system and how measure system pressure. But yes you still can save couple backs! ))