Lay down a 4" thick square bed of asphalt, say 20'X20' in Texas or 30'X30' in Minnesota depending on amount of heating needed, with 1/2" copper flexible tubing in the middle. Tamp the last 2" lightly as possible and with great care.
Connect a water source to one end and say a swimming pool to the other end and "voila" your heat engine is ready to go to work.
If you get a lot of ice accumulation in your part of the country, you may want to think about temporarily covering this asphalt pad with a few inches of wood mulch prior to anticipated accumulations