wrote:

|A larger tank should help, given a smaller surface to lose heat from...
|
| Larger tanks have less surface?

As the volume goes up proportionally to the cube of a dimension, the surface
area through which heat can escape goes up only proportionally to the square
of a dimension, assuming a constant shape (e.g. ratio between diameter and
length for a cylinder). A tank which doubles in size for all dimensions
will have 4 times the surface area (where the heat escapes), and 8 times the
volume (where heat is held)...

A lovely explanation, but as you write above, larger tanks
have MORE surface, so larger tanks have MORE heat loss...

Nick