Racks are easier to control and maintain in warmer rooms (cool being below 68ºF) they become difficult to control ambient air temps below this. I would recommend a failsafe T-stat on all racks (questionable if using the HS1 or better with a relay and over and under temp protection) it will protect against a sudden drop in temp and shut off power rather than try to maintain heat. Sudden drops happen when the probe is pulled loose somehow, this can happen sliding tubs over probes.