Rack not warm enough?

[Pecan'nPumpkinPython]

I am so excited! I finally got my new rack, but I am having a hard time getting my temperatures stabilized and up as high as I need them. The rack has four 32qt isis brand boxes, is heated by 3 inch flexwatt for belly heat, and is hooked up to a Ranco thermostat. The temperature in the room it is in is about 75-76 degress, and the cold side of all the boxes is stable at about 79-81. The problem is that I can't get the warm side temperatures up high enough, and that the warm side temperatures are varying from box to box. I have the thermostat probe directly on the flexwatt on the second level, and my thermostat set to 104 right now with a 1 degree differential (that seems a bit high?). Yet the warmest of the boxes (the two in the middle) are only heating to about 89-90. The boxes at the top and bottom of the rack don't appear to be heating much at all, with temperatures consistiently in the 81-83 range. I have let it stabilize for two days now hoping that would help, but I am really wondering what I am doing wrong now. Thanks in advance for the help.

[Freakie_frog]

First where are you getting your temps from in your box.

[Pecan'nPumpkinPython]

I am taking readings with an accurite and with a PE1 tempgun near the back of the boxes almost directly over the heat tape.

[grunt_11b]

Bump having similar problem... I just put 4" heat tape in my rack and I'm having the thermostat at 102 to get 88 degrees in my tubs????? Any help will be appreciated....

Alan