Re: shop heating
If you have concrete and want to put in floor tube heating you should tear out the current concrete. The system is too expensive to not do it correctly. Protect your investment. If done correctly a reflective insulation is rolled down first. A sheet of wire mesh is then laid down to attach the tube runs to and then rebar is laid out on top just like you would for a normal concrete floor. In floor heat will be the most expensive upfront install by far.
Radiant tubes from the ceiling or forced air (any fuel) are your best options if you can't part with your current concrete.