Planted Tank Obsessed
Join Date: Apr 2013
Location: Coastal Georgia
Tank size will have little effect in a larger scope of things. They simply are not efficient for this particular task.
For the same price you could get a window AC unit for the room, and it would cost less per month than the fridge to boot.
Yes insulating the tank walls would work. If you could take a thermal image of your tank on a hot day (with colder water inside) you would see the cold falling off of the sides onto the floor. Heat rises out of the top, just the same as taking your hat off in winter and seeing the steam rising from your head. Glass is also a really poor insulator compared to other materials.