Track, I use a hydrofarm for a tank setup with an Ultratherm UTH and it stays within 3-4 degrees regardless. I also use one with my flexwatt under my tubs and it will go up or down depending on the temp of the room. I know it's not the same setup as yours but if I set the hydrofarm at 100, I get a hotspot of about 90 in a cold room. If I warm the room up I will have to adjust the hydrofarm lower because the hotspot gets to 97 or higher. Hope this helps.