Last week or so I've been working on the completion of my little barn. I like working with concrete as a material -- pourable stone, what's not to like? -- but this particular little slab has been pretty complicated.
The reinforcing mesh will make the slab resist cracking and settling, and is just what you need to tie the pipe in. Here I'm using zip-ties. they won't damage the tube in the future.
The reason I'm choosing to do this is that this area will be a working area, and will contain pig equipment and gear, as well as water supplies for pigs housed here.
So here's the basic theory on radiant floors: The concrete slab will be heated by liquid run through the tube; this heat will radiate up from the slab, providing an even, pleasant heat without hotspots, or the need for radiators or other ductwork. Since I'll be using this space as a barn, and scraping it out with a tractor, having a smooth, impervious floor and clear space is a big plus. Now I don't have to use the heating ability of the floor at all -- if I choose not to, I've spent $200 or so in vain. But short of ripping it up and messing with it, when you pour the slab is when you do this, so I'm putting it in now to keep my options open in the future.
For a low-temperature barn -- say 50 to 60 degrees -- you can use a small water heater, a pump, and a low-temperature thermostat to keep your building comfortable. The water heater is on at all times; when the thermostat detects low temperatures, it starts the pump, which continues until a pre-set temperature is reached. the water heather, pump and floor are on a closed system, which if I do this will be filled with a non-toxic mix of water and antifreeze. (I don't want to have to worry about the liquid freezing in the heating system, and I don't want to have issues with animals drinking toxic antifreeze. )
A second option is to mount a solar collector on the roof. Have a pump switch on when the water in the collector hits 100 degrees (which you can get to even on a cloudy day). While the pump is running it's circulating the water water through the slab, transferring solar heat into the mass of the slab. After dark the pump switches off and the slab then releases its heat gathered during the day overnight. The next morning the process repeats.
This is basically the same thing that a heat pump does, but I can't bring myself to pay thousands for a heat pump. A little 12 volt pump, a few solar cells, a couple of temperature sensors and some copper pipe and lumber makes a perfectly workable system that costs a few cents a day to operate.
What's all this cost? The insulation is actually the most expensive; it's $15 per 4x8 sheet of 2" material. it's R7 or so, which works for my purposes. the reinforcing mesh and gravel I would have done with any slab. The tubing is $0.60/foot, and to do a 20x20 with tubing at 8-9" centers took about 320' of tubing and a coupling. You'll want a pressure gauge and cap to test your system to make sure its airtight before you pour; that costs about $20.
Total cost to put in radiant floor heat option: about $1.20/square foot.
For a discussion of pressure testing the floor plumbing and a discussion of the types of tubing used, check here.