Size of UTH?

[dadykhoff]

I have always heard 1/3rd of the base of the tank..

If you look right on the packaging for the UTH it usually says 10-20 gallon, 20-30, etc.

It can also depend on the room temperature. Sometimes lower ambients call for a bigger UTH to raise the ambient tank temperature.

Okay, so if my ambient room temps are around 70F, should I go with 1/3 of the base or go a little bigger? Thanks for your response.