Mine is 30×60, and we put hydronic heat tubes in the floor when we poured it. I heat the water with a cheapo Menards water heater. I embedded the temp probe in a tube in the slab, so the thermostat works great. We have no water supply to the shop, so it’s a closed system. The whole system cost under $1000. We keep it at about 50 degrees, and it costs about $300-500 to heat it for the year. I’m hoping to add on either a solar collector or an outdoor wood burner and then I plan to run it at 65 degrees or so. Heat rocks.