What size box do I use?

Let clear the air...I am well aware that fish do not need ventilation.

Most of what I have read concerning the holes in the box was for oxygen to react with the heat pack and not for ventilation for the snake.

Again the snakes I have received via shipping had no holes in the box so my question again is..is it really necessary??

Is it necessary? Maybe not. Do two 1/4" holes, on opposite sides of the box (4 total) hurt? No.

Do 1 inch holes hurt (I have seen this)? Yes. Too much air flow, compromises insulation.

The few times I have seen issues with heat packs failing, it has been with no holes. It is assumed that the heat packs use up the available oxygen, but I have no proof of that.

As for fish, there are breathable fish bags that do an oxygen exchange, so theoretically, it COULD cause an issue : )