Fluidmaster makes a waxless seal that would work for that. We push the adapter onto the bowl first, and then set the bowl over the flange.
I just finished taking the tile off the bathroom floor in order to get it ready for the new tile (and heating cables)!
the toilet flange is sitting on top of the plywood right now and in decent shape... some water must have leaked since the wood is discolored just a tad around the flange
but aside from that it seems fine..
Normally I would install the flange on TOP of the finish floor (i.e. the tile). but can I get away and leave the flange that is there and install something like this
if I go this route, the finish floor would likely sit 1/2 inch above the top of the flange...
the fernco toilet seal would be long enough to still get a good grab ...I think...would that be ok or do I need to remove that flange?
oh and putting double layers of was seals is not an option for me since I'll be doing in floor heating...
removing the flange would be a pain in the butt since I don't really have access from below... I would need to cut out the sub floor.. I rather not if there's an alternative
The Fernco waxless seal looks quite similar to the Fluidmaster, so I would expect it to work well. I don't know what the installation instructions are for the Fernco, but I would stick the flange on the toilet first then set the toilet. Fluidmaster's instruction sheet is best used as toilet paper. I've tried it both ways, and putting the seal on the toilet first is by far the easiest.
Manufacturers of in-floor heating systems recommend keeping the heating cables away from the flange; Laticrete says at least 4-6 inches, while NuHeat says 6 inches from the center of the drain. I have a hard time believing there would be enough heat build-up under the throne to melt the wax unless you had the temperature cranked to the 100+ degree range and ran the cable right next to the flange. Another alternative is the el-cheapo flange extenders that you stack on the existing flange (with silicone sealant between the flange and the extender).