Heater size for tanks

Looking into designing my betta breeding setup. Will be using either 10Gs or a divided 20L. Have to use a heater in order to maintain the required 80F temp.

Would a 100W submersible suffice for a 10G or 20L? I will be bubble wrapping underneith and on three sides for insulation.

man i have a 50watt hydor in my 10 gallon and it does just fine, 100watt might be over kill

3-5 watts per a gallon is what most people use.. also depends on the heater use a good heater and you could get away with lower watts... I like the hagen, and theebo jager.