Thanks, franztini, for taking time to share your thoughts. I agree with you- Warmboard is great for new construction, it would be quick solution. In your situation, you probably already have some insulation in the slab from your previous radiant heat. My slab has no insulation at all. It is desired that insulation over slab has R=19. This would require 4" thick insulation. I can't raise floor that much and would be ok with R=10 (maybe even lower). Roth panel seems as a great option for slab since it is made of insulation. Also, aluminum on top may heat floor faster. Though, for some reason, I have tough time to find contractors in NJ that have experience with Roth panels. Also, comments related to Roth panels I saw on web seem to be older. I was wondering if there were any issues with RP. The drawbacks - it may be time consuming to install (especially for hardwood flooring) and R value is only 4.5 and no additional insulation can be added underneath. Though, I would still consider if people have good experience with it. Also, there could be some additional tricks to improve insulation such as insulation on perimeter (don't know much about it). I looked at HeatPly. Because it is made of plywood, I would need additional insulation. Also, you may note it doesn't have the benefit of having aluminum on top to heat floor faster. Though it is great that it is provided with boiler and tubing. If you don't need insulation, it may work well for you. I found out that in order to insulate under Warmboard, I would need to use sleepers (rigid insulation will not work). While this will be the right way to provide insulation, this will require raising the floor level. I am taking time to make the right decision but have really hard time with it and the cold weather is around the corner.

I would not be too quick to sell that liquid bonding material short. Back in the early 80's I was working maintenance for a large municipal school department and we an area where we needed to use the tubes of liquid nail, but like you, we were a bit skepticl of how well that stuff works, so we decided to give it a test. I took a 4' piece of 2x4 and cut off about 6", then I used the liquid nail to sister the cutoff piece to the side of the remaining 2x4 on one end and I put it in a vise to clamp it. I left it in the vise overnight, and the next morning I took it out and clamped the short piece in the vise and tried breaking the joint by both lifting an twisting on the longer piece of 2x4. After two of us grabbed the 2x4 and pulled on it as hard as we could causing a twisting force on the joint, the joint finally failed, but when we examined where the two pieces of wood had been joined we discovered the glue had not failed. The wood on the shorter piece of 2x4 had split amd sheared away, which accounts for why the joint finally failed, but the actual wood to wood glue joint was still intact.

I am about 150 miles south and just pulled out all tile and carpet replacing with new tile throughout except 4 bedrooms. i entertained the idea of polished concrete... love the look. But decided on tile and glad I did. Once everything was pulled up, found surprises. Cracks, funky chipped away part in three spots, and at some point some portion had linoleum or something (black glue gunk all over). Plus, if house is built right you should have expansion openings (the are called something fancier). If/when you tear out tile, be sure you have a budget to replace if needed.

There is no reason your idea won't work. If you get incentives for energy conservation you might consider solar heated water circulation in addition to electric strips. There's plenty of room for both. Are you handy? Check out a site called "Build It Solar" for some great diy plans.