Originally Posted by howell_jeep
How does floor heat work? What is the energy source? Can it run on propane or does it have to be a wood boiler of sorts?
Google will tell you a lot on the subject. Try searching garagejournal.com as the site.
With in-floor heat, its heating the whole mass of the slab, so very good if you plan to keep the place heated full time. Its not going to quickly raise the temp of the building, but its very even comfortable heat, especially if you are crawling around on the floor.
You would definately want to insulate the foundation, ideally running 2" foam outside of your rat walls (assuming you are doing rat walls and a slab, not a full footer foundation) down a couple feet, and out a couple feet, then foam under the whole slab. You can always put all the foam and tubing in, and then add the boiler/heater/manifolds later, although most of the cost is in the insulation and tubing.
I didn't go that route, because I had X amount of funds to work with, and putting that ~$3000-$4000 into the shell let me get a 20% larger building. And because my barn is intermittant use. I might not be out there for 2 or 3 weeks, so I don't want to heat the barn for that whole time for 5-10 hours a months. If you are someone who spends their evenings out there as the man-cave hang out, then I would be doing the in floor heat.