My shop is 75X36X12 with partition at 14 ft. 12X12 panel door and 36" man door. There is shower, toilet, guest room and office/workout room in the partition. I have sink and hot water in the shop. The guest room and the office are heated/AC by two zone mini split. The shop has 6" slab insulated by 2" pink closed cell insulation, has about 18x25 concrete apron outside of the door. 9" R-19 insulated walls and and R30 insulated ceiling. Shop has no windows and is finished in metal inside (I was the cheapest option). All electric wiring is in conduits outside of the walls. Air, 220 and 120 V outlets every 6 ft on one long wall. The shop is heated/AC by 36000 BTU mini split. Originally I wanted floor heating with a heat pump but then decided to invest the money in solar panels and use the mini split and baseboard heat as backup. Problem with PEX in the slab is that you might hit it when anchoring something to the floor. Shop has wired and wifi ethernet and is connected to the house network.
I think the mini split heat pumps are way cheaper to operate than floor heat with a water heater.
1.) The time constant of floor heating is measured in 2-3 hours/deg (I know it because we have it in the house) while the air heat is about 5-7 min/deg even when it is cold outside. In other words the floor heat has to be more or less set to constant higher temperature all the time while I maintain 50 deg when not present and up it to 65 when working there. Since the mini split inside unit is in the middle of the long wall it blows warm air pretty much where the action is.
2.) The mini split heat pump is at least twice energy efficient than a water heater.
3.) Floor heating doesn't do AC.
4.) The minis are very quiet.
5.) Most utilities will pay you energy efficiency rebate for the mini.
Mini split cost from mail order 3600, minus 450 rebate plus 180 to commission it. I did all the installation work, the HVAC guy only connected the lines and vacuumed it. 2 hours of work including travel.
If I do it again I would go to 14 ft high and make the door 14 wide. I am changing fluorescent to LED instead replacing the non working tubes.