I believe the six watt is the recommended rating, I have 4" 8 watt on my racks and those tubs (the dimensions you gave match the Vision V-35's) if they are the Vision tubs they sit real close to the bottom surface and heat really well so 6 watt should be fine.
yes they are vision tubs. so 6 watt will be enough? what about the vision v-70?
If you have a good quality thermostat such as Herpstat or Helix that can do proportional heating then 6 watt will be fine. From what I found when I looked into buying a rack is that some of the PVC racks use the same 3" heat tape on those big tubs. That didn't seem to be enough in my opinion, but there is the animal plastics 41qt rack that has a dual side heat panel option. Most of the opinions I received when I asked around were that folks were generally using the 11" flexwatt for the adult racks with 41qt tubs. When I make my 41qt rack I'm going to use 11"
Last edited by Steve-J; 12-03-2011 at 09:48 PM.
Reason: forgot something