I intend to finish a part of my basement following this guideline from Fine Homebuilding and Building Science. There are two options I could come up with for installing hydronic radiant heat extrusions, and I can't decide which of the two is most ideal.
Option 1 – Route out a pathway into the insulation that would fit the aluminum channel, then cover with the two layers of 1/2" plywood, then cover with flooring
Option 2 – Start with 2" foam, put down 1/2 ply screwed into the concrete, put down aluminum channel on top of 1/2" plywood, cut strips of 3/4 plywood to go between channel, install flooring over 3/4
Option 1 is much easier to build. The foam will have some "give" when fastening the plywood against the aluminum plate, which will ensure contact and allow flatter flooring layers above. I just fear the aluminum on insulation contact, movement and directly heating the insulation. There are adhesives to secure the aluminum to the foam if that's appropriate.
Option 2 provides more "structural" support to the channel to prevent noise, as well as providing more thermal mass and more isolation from the insulation. I'm not sure if the layers of plywood will have enough "give" to encapsulate the aluminum track without causing the surface to bow.
Best Answer
For a ThermoFin U extruded aluminum heat transfer plate installation on concrete, you would build a surface to be able to screw the plates into by first putting down a layer of Atlas Rboard®, recommended 1/2", which you should be able to get from your local building supplier. A Google search on Atlas Rboard® will bring up their site and the product info.
On top of the Rboard® put down a layer of plywood. The fasteners will hold best if you can use 3/8" plywood. It will work with 1/2" plywood if necessary.
Keep in mind that you want the heat energy to be going into the sleepers and the finish floor, which is why we recommend the Rboard®.
The energy without the layer of insulation will be drawn into the concrete, and the response time would be longer in heating the floor. Heating up the mass of concrete is not necessarily a good thing when you want the entire surface floor to be warmed.
Radiant Engineering aka Radiant Design & Supply has decades of success with ThermoFin U and ThermoFin C installations in North America. Install ThermoFin U with the fins facing down for wood finish flooring. For tile or stone, install with the fins facing up. The sandwich of aluminum and plywood provide an evenly heated surface that is friendly to finish flooring installation. ThermoFin U specs are .050" gauge, width 4", length either 4 ft or 8 ft, tubing channel size either nominal 1/2" or 3/8".