I won't do the calculations for heating with propane vs electric. If you are going to heat with electricity why heat water first? Can't the electric heat be buried in the slab? If for some reason some other fuel source becomes less expensive, install forced air using that. On the other hand, a heat pump producing hot water could serve you better in the long run for radiant heat in the slab. I am not an expert, but my impression is that is more a commercial-type installation. I know that Mitsubishi City-Multi systems and similar from other manufacturers will make hot water, but they may be too big for your building. There are probably other options, but they might be outside the experience of a strictly residential installer. Carefully consider building orientation and window location for passive solar heat in winter. If you have good insulation and other efficient features, a high efficiency heating or cooling system is less important and you will have to invest in smaller mechanical systems.

i'd like to add a few points. A slab is a thermal mass bigger than an elephant. Concrete is a heat sink. You do get all the heat back, if you own both sides of the slab. In that case a concrete slab is a heat source as well. A governor. Here you don't have that. A slab on grade is connected to mother earth. The more it acquires heat (from any source above), the more it loses heat to the ground underneath. The more you try to heat it, the more you spend on heating the earth underneath. That is a lot of mass. This explains why seeds germinate next to rocks. The rocks acquire heat from the sun and re-radiate that heat into the ground, triggering germination. Your slab on grade might be on earth that is generally dry and warm. Or not. The more moisture in the earth, the more slab heat is lost to the earth. More quickly. It may be easy to have a warm floor on a warm slab on grade. Do nothing more than install wood on an underlayment. It's difficult to turn a cold wet slab on grade into a warm floor. A layer of really good insulation is required. Now, you are walking on a raised floor. Since you asked about the new and thin electric heating cables, I'll guess that you can't raise the floor by much.

oh well rub it in why don't you! :) We actually don't get a lot of pouring down rain where we live, but lots of drizzling. As far as the water issue, pumping is really not an option at this point. We have all the tubing and foamboard installed/stapled. Hubby says it will be ok... just wondered if anyone knew for sure. :)

Thanks...I try. Too many people *think* a concrete floor is a money SAVING project. It is not. A SLAB floor is money saving. It is ugly, unfinished and can be very rough on the feet. A properly finished concrete floor is beautiful but very expensive. Most people think slab concrete is the FINISHED floor and therefore cheap. What they do NOT appreciate is how UGLY it is and how much it stains and etches and degrades over time (chalky dust on the surface all the time). They are very disappointed in a SLAB floor. When they are told the cost to fix a concrete slab floor they look at the refinisher like they have 2 heads and say, "Well if it's going to cost me $10/sf why don't I get hardwood and be done with it?"