I also use 3 inch Flexwatt. I use 32 quart tubs at the moment and with the 3 inch Flexwatt I have a steady 84-85 degree hotspot and the rest of the tub stays right around 80F, depending on the room temperatures. If you're looking at T-stats to buy, I highly recommend the Herpstat. They're well worth the money and I don't think I will use any other brand.