Electric floor warming systems are for floor warming only. They do not heat the room. If your slab is uninsulated, then in your cold environment your floors won't even really get warm as the heat will be sucked out through that slab into the outdoors. It'll be a waste of money. I'm really surprised that you actually have slab construction in such a cold climate. Slab requires footings to be dug down below the frost level so it won't heave, and in your area, that's down low enough that it's not that much further to do a basement. And to do a slab without insulating it is also strange. I would not put hard surface flooring in such a situation where you cannot install the sleepers and additional insulation. Your best bet for comfortable flooring will be for carpet. The padding will give a small amount of insulation between you and that freezing cold slab.

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.

Your HVAC expert who is designing the system should explain the requirements that the manufacturer has for their particular system. In general, in your situation, you will need lower temperature loops closer together rather than the traditional higher temperature loops further apart. The whole system has to be designed for the water temperature that you will need, as well as the PEX placement distance. Floor coverings also has to be taken into account in the plan. Rubber and carpet actually have insulative power (R values), and are not conductive to easily passing the heat through into the home. That has to be calculated when designing the system, and it will increase the lag time to temperature changes, which is already radiant's biggest drawback.

Tiles are hard. Done. We know this. Wood is more forgiving but still rigid. Cork is very forgiving BUT it doesn't do very well over in-floor radiant heat (the cork is fine....but it can block as much as 90% of the heat moving through it...makes for a cold space). Rubber may or may not be allowed over in-floor radiant heat. Some of the low end rubber will give off a heavier smell when the heat is on. I'm sorry to say but the best option for in-floor radiant = tile or carpet. Since this is a kitchen, carpet is out. I've had enough people use cork over in-floor radiant and most of them come back saying the cork is lovely....but the space gets too cold. The heat doesn't move through the cork enough to heat the room. Feet are NICE and warm...shoulders get chilly. And a traditional cork floor in a natural finish will do rather well with dogs. It's hard to see scratches on natural (oak coloured) cork. Very hard....The issue for me would be the cork blocking all that lovely heat your floor is producing. And there are many floors that I would recommend for comfort....but the in-floor radiant heat is going to get in the way! Sigh. This is why I have a bit of a hate-on for in-floor radiant. It reduces the options. And when it comes to body pain/foot pain, the wider the range of options, the better chance you have to live a comfortable life free of pain (which cork is REALLY good at). Leather, seen below is a traditional colour that looks very handsome. Silver Birch (above) is another cork floor that looks like bamboo/narrow strip hardwood. Either of these patterns will work in a home where there is someone who isn't sold on the look of cork.