Heating

Wait till it's cured, at least 30 days, and then the heat has to applied slowly so the concrete and the tubing isn't stressed. Let's say your design slab temperature is 85F and you are starting from, say 45F. It may take a couple weeks - start with water at 50F and increase in 5F increments every 3-4 days till you are within 5F of setpoint. Monitor with your slab temperature sensor(s) (you DO have some slab temperature sensors, don't you?) so you can see if you can increase the temperature at a faster rate. That's my conservative P.Eng recommendation that is safe. Others can go faster but the slab internal temperature must me monitored so you don't have a high differential betweem the heating fluid and the slab.