Ply wood on wooden floor

Hi, Check on heating manufacturers website for suggested insulation. Usually it’s ply or a board on the floor, fixed with screws that go into the material (doesn’t damage man) then the mat, stuck down with the cables etc fed through the points, flexible adhesive on the tiles and heat not to be used for a week till it’s set.

I've never heard of anyone stapling down ply ready to tile on. How thick is the ply and what is he fixing the ply too? Insulation boards tend to be fixed down with screws which have round plates to stop the screws going through the material. I would only use adhesive if the floor was uneven with bumps and dips here and there. Although there is no harm doing it all the time. I would lay it brick bond style; 90 degrees to how the ply is laid. After laying the UFH matt. You would want it self levelled to ensure all the wires are covered and you have a flat surface to tile on. 100% coverage is needed. Flexible (Rapid set) cement adhesive and grout should be used. Read the manual regarding how it should be turned on. On one I completed before said to wait 24hrs, then to turn it up 5 celsius every day till you reach a temp that you like, and then to reverse the process till your back at 0. Another one I completed said to wait 48hrs and then it can be used as you desire. They vary, but if unsure, I always recommend the 5 celsius technic to be safe than sorry.