I’m renovating an old house and have to lay down 3/4″ ply on tapered 2x shims to level out the floor. I may jack the floor some, but I doubt that I’ll get all of the shape out of the floors.
I’m interested in heating the place with under floor hydronic. My questions is…Will having an air space (between the new plywood where the floor is shimmed, and the old plank subfloor) reduce the effectiveness of hydronic tubes under the old subfloor?
The air space may be as much as 2″ in some places. Is radiant heat just not appropriate under these conditions?
Replies
Run the heat tubes above floor. You can purchase grooved ply panels that can be used as you new subfloor, or add 1/2" ply sleeper panels on top of the 3/4" to provide the channels for the PEX tubing.
The few floors we worked on for customers with wood framing, were not as drastic as yours. We were able to level up the newly opened up areas prior to hose install. Working off of a leveled subfloor we ran strips and loops of 3/4” osb that we applied the aluminum “shields” with grooves for the hose, topping it off with an approved “pad” (meant for radiant) and then floating engineered hw flooring. This system kept the hose even and the aluminum plates dissipated the heat evenly.
This system was again, on top of a subfloor vs layer under and between the joists.
As to whether or not your heated floor would even out? I don’t know.
What finished floor are you putting down?
I'm a little hesitant to respond here, as this is not an area where I would pretend to know a lot about the science of heat transfer, however, I've built and lived with radiant systems in a few different setups.
As I read it, the existing subfloor has radiant under it already and you plan to shim it up, creating an air gap of up to 2" between the existing and new floor. I would say, this will adversely affect the heating of the floor. If you can't change the existing setup, you might want to consider filling the void with something like sand, which will create a thermal mass. It would slow reaction times (both heating and cooling), but I think create a better heat transfer. I have a similar setup, although my Pex is embedded directly in a 3" layer of sand between subfloor and tiling.