When I was installing my pex staple-up, I was told by an experienced guy to install the aluminum conduction plates.. I didn't want to, because of the
But he insisted.. So I experimented,, and he was right.. [Thanks Sting !!]
This was new construction, so I had bare plywood on top [the floor surface] and fresh joist spaces to work with.
I ran one joist space with pex only, the next joist space with pex and foil faced insulation, foil faced up with 3" air gap to the pex.
The next joist space had 8" wide aluminum radiant/conduction plates over the pex, the 'bump' over the pex was a simple 'V' made with a siding brake.
The fourth joist space had aluminum plates and insulation, foil faced up. 3" airspace..
I took my laser 'no touch' handheld thermometer and went over each joist space from above and noted the floor temps.. this is 3/4" plywood.
There was a HUGE difference from space to space.. the pex-only had a narrow stripe of warm floor,
The insulated pex without radiant/conductor pate was better, but there was still a heated stripe.
The third space, with conduction plates, no insulation was much better, the heated stripe was MUCH wider, and floor hotter.
The fourth space was the best, virtually no 'stripe'. I could find the unheated joist, but the entire joist space was evenly heated, and the floor hottest.
So, I bought aluminum flashing in rolls from Home Depot, and bent up radiant panels to put over my 1/2" pex, and insulated the spaces.
I proved to myself that the aluminum panels vastly improve the transfer of heat from the pex to the flooring..
On my main floor which is a 1.5" concrete suspend slab over 3/4 plywood, the basement below does benefit from the warm plywood, surprisingly,
the plywood is around 65-68*, the slab and slate above usually at 74-75*. The radiant from the ceiling works well to heat the basement,
so I have not yet hooked up my radiant in the floor slab, it is 4" insulated on pea-gravel..maybe one day..
Once I get the slab heated, I'l insulate the floor above with foil faced, but for now it works.. and I'm lazy..
BTW: here is the link to that 'Huge Project': My current huge project
I'm damned glad I got that project mostly done a few years ago, I'd not be able to do it now..