OK...for the scary answer...it doesn't matter.


By this I mean you need enough holes to create air flow, but not enough to lose all your humidity and heat. So I am sure your next question is then how many holes...the answer is NO ONE can you tell you. You have to experiment. Start out with a few holes (4-5 on 2 sides for a small tub/7-8 on 2 sides for a large tub - this is just a guess and starting point)...I would recommend you start on the sides where the air flow would be coming from. If you have no flow (a fan, vent, ect.) then what end you put the holes on doesn't matter.

The benefit of a tub is that is you don't have enough holes you just burn more...if you have too many you can use tape (on the outside of the tub) to close some up. You will find most likely that you need more holes in the summer and less in the winter.