HI David, welcome to Fishlore.
What size sump are you using?
I aI'm for about 3W per gallon. So that's a minimum 400W (ish) you'd want, but you also need to add sump volume into the calculation.
You also need to consider the ambient environment and your equipment. If you're in a warmer environment, you might be able to get away with less heating... Heaters generally work on being able to heat x volume of water by y degrees above ambient in z period of time. Even heaters that have temp settings have limitations.
You're equipment will also add heat to the water as they use the water for heat transfer to keep them cool.