Wh00h0069 asked,

How hot does 11" 20 watt flexwatt normally run?

I did a test for you.

With the heat tape running full power in a room that was 79 degrees, I was shooting temps from 107 at the coolest spot to 131 at the hottest. This was 11" flexwatt, temps shot directly at the surface with an infra red gun. The heat tape was uncovered and laying on a piece of pvc sheet. I let it stand about 20 minutes to stabilize before shooting temps.

I have a back heat rack with 11" heat tape that works just fine. I can maintain my basking area in the rear quarter of 12 qt tubs at 90 degrees in a room as cool as about 72. At that point I am sure the flexwatt is receiving full power from the t-stat trying to keep up.

I suspect the larger tubs may be a little harder to heat. How far from the heat tape are you measuring the basking temps?

One thing I would recommend would be to put some reflective foil behind the heat tape. That is between the melamine back panel and the heat tape, with the reflective side toward the heat tape.

I think you might be surprised at the difference this makes.