What is the proper wattage for a CHE in a 4'wx2'dx17"t melamine cage?

[Theleveler]

Hi guys,

I've been using a 150 watt CHE for my 4 foot by 2 foot by 17" tall melamine "critter condo" type cage that my 6 foot adult boa lives (sleeps and eats) in. I find that the thermostat is off roughly 50% of the time on warmer days , which makes me concerned about possible thermostat failures that would stick in the ON state. Should I be using a 100 watt ceramic instead? I'm using Eco earth, if that matters. Temp and humidity targets are very stable now (78coldside-88hotside-92hotspot; 60-80%humidity depending on shed cycle).

I'm planning to build her a bigger cage in the future with something fancy like RHPs, but for now I'm stuck with CHEs.

Thanks!