Hot water heat
I have in floor heat in my slab. I highly recomend it. Last years heat bill in northern Iowa was $43. Very important that you create a insulation bowl so to speak. I have 2" pink high density foam on the bottom and up to the pour line or concrete height on all 4 sides. I installed the plastic heat tubing in 3 zones. ( garage is 24X36). also important is to keep the zones nearly equal in length. This keeps one from getting hotter than the others. I ran the tubing about 12-14" apart and fastened them to the foam. Poured concrete over the top. I heat the water with a small boiler hanging on the wall. The name of the boiler is Munchkin. It will vary the burner output to match the water temp drop of the circulating water. Fill lines with antifreez ( I used RV for environmental concerns) and away you go. I have heard from others who used a water heater. The problem they had with those was needing to create a control situation that would turn the heater on and off or leave on and it will keep the loops and tank at a set temp. You will also have and additional water in tank. You will need to control a circulating pump also. The boiler idea has all the controling incorperated and is operated from a wall therm. Set it and forget it.