Thanks for all the input; it's been really helpful. Shanghaimom, I did a 'step test' with a 12x12 marble sample I had on hand, and you're right; it is so much colder than the tile. That has convinced me to install floor heat, even if it's only a secondary source. I had no idea that hydronic toekick heaters existed; the quotes I got all mentioned 'electric fan toekick heaters', and I didn't want to go that route. When discussing with my contractor last evening, he was very supportive of the hydronic solution; now I just have to make sure that the unit will fit under the 'door' side of my vanity (will need to access it for service, so it really shouldn't creep into the drawer side of the cabinet.) Fingers crossed! Mongo, thanks! I'll do my homework on the BTU calculations; thanks for pointing out what to look for. Lynneblack, thanks for the vent/fan/light combo idea. I've read on the boards that the Panasonic is a great unit, but one of the two items I'm keeping from the current bathroom is my Nutone melon vent fan/dimmable light.

There is no practical technology for passively shielding a heating element to virtually eliminate H-field EMF. The only effective approach is "active shielding". This means canceling the H-field of one heating element with the H-field of another parallel element. Watts Radiant electric heated floors use this approach with a complex wire made of two sets of heating element constructions; running them in parallel with a patented helical twist. Here is a link that might be useful: Electric Radiant Floor Heating

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.

The house I am currently building is ICF, and I love it. I considered SIP's, especially steel SIP's, but it wouldn't have been feasible for one old man (me) working alone. I went with a conventional wood floor structure and roof trusses. I did build everything to FL wind standards, even though I am in upstate SC. If money were no object, I would have still used ICF, due to the structural strength, but I would have done a suspended concrete floor, and used light steel framing for the roof, with steel SIP's for the roof. Not only rodents, but termites have been shown to tunnel through the foam for considerable distances. Either critter can get through a conventional OSB SIP, and of course, ICF, although they can't get through the concrete in the ICF to actually get inside. The reason for all of the steel and concrete is that it doesn't rot, burn, or get eaten by anything. Also, wood quality these days is dismal. It took me a LONG time to strap and shim my ceilings to get them flat. I used steel framing for the interior walls to get them straight and flat. The inside of the ICF was already perfectly flat. BTW- there are fastening points every 8" with ICF, so attaching drywall and other items to the wall is as easy, or easier than wood framing.