I have 4 ut heaters and aluminum foil on the screen lid.
My adult female is just fine.
She weighs over 6 pounds at this time.
I have 1 uth under my water dish plugged in 24/7 and the remaining 3 uth are on a thermostat.
my thermostat is a "zoo med reptitemp 500R" it is a lower end unit but it does work just fine however.
even with a thermostat I have to "turn it up" in winter and "turn it down" during summer.
my BP's tank is upstairs that gets cold in the winter (some times 41 degrees) , don't worry it is nice and warm inside her tank....
some times I wish I had a higher end unit, the perportional kind, but they cost over $110.......
Harry