There are farmers here in Iowa who heat large insulated pole barn building/shops with nothing more than a 100 gallon hot water heater and in floor Aqua Pex flex water pipe tubing. It is also used in new home construction. Running a 1500 watt hot water heater for the winter is much less than propane. Once the slab is warm, it is easy to keep it warm. Takes very little power. There is a company here in Dyersville Iowa called FarmTek that sells all that you need to set up a system. You would definitely want to put a radiant barrier down on the soil then the insulation, then the re wire, and fasten the tubing to the re wire with zip ties. I did it in a sunroom addition on my house.
Tom....
Tom, you are making some pretty big assumptions on that one. What I mean is, it all depends on your electrical rates. Here in Maine we pay some of the highest electrical rates per KW in the country...something like 18 cents a KW. You could pay up to 4 bucks a gallon for propane and it would be cheaper then using electrical heat.
As with your theory on water heaters, that is another wolf in sheep's clothing. At first it looks inexpensive and efficient, but in reality it is not. When I did the radiant floor heat in my new addition I went through all the potential ways to heat my house. Ultimately a boiler is the best way to heat water. here is why.
With a hot water heater, you are using 180,000 btus to heat that water to 120º. With a boiler you use only 80,000 btus to heat the water and to any temp you want. It gets kind of hard to understand, but by using the right temp sensors in the concrete, outside and boiler water temp sensors, my controller can adjust the water temp flowing through the slab to heat my house at the LOWEST possible temp. Most days that is around 86º, but it goes up and down with the temp outside. Meaning if it gets colder out, the slab will lose more heat so it adjusts by increasing the water temp flowing through it. If the temp rises, it lowers the water temp running through it so you don't waste heat and btus on using more heat then what is needed.
So why is this so much better than a water heater...even a propane power water heater? Its because you are not overheating your water. Why use 120º water to heat your slab when only 86º is needed. That extra degree wise is wasteful.
Please don't think I am talking down to you here. It took me three separate conversations with my plumbing dealer to understand why a hot water heater was inefficient and overall more expensive then buying the boiler. The thing to understand is that its the whole system that makes everything effecient, not just the boiler. The controller, the plcs, the sensors and the flow valves all work in unison to ensure it uses the least amount of btus possible. Its the btus we pay for and that does not matter if its electric, propane, natural gas or wood. We buy btus.