I’m installing radiat tubing in the floor joist cavites of my first and second floor addition.

I’ve been advised that I need to use aluminum transfer plates with the tubing for maximum support and heating efficiency. I’ve also had people tell me I only need to attach the tubing to the underside of the subfloor by whatever method, then insulate the top two or three inches of the cavity to insure that the warm air there moves up through the floor, and does not fill the cavity and the ceiling of the room below, wasting heat.

What’s the best practice? How much heating efficiency am I gaining or losing either way?

Confused. Thanks.