how big the vent holes be on the incubator?

[Chickenfarmer 1-2-b]

I am about to finish the incubator. Just dont know how big the vent holes should be. Also what is best to use for cutting the holes? I am using the styrofoam ice chest. Thinking of putting 4 vents holes in. any suggestion is appreciated.
Thanks.

 

[seminolewind]

I would say about 0.3 inch. With a plug. You might want to put a 2nd hole in there.

 

[The Chicken Lady]

 

[CajunChick]

I used an apple corer...not the kind you push down on the apple though

It kinda looks like a vegetable peeler. It cut perfect holes in the styro and you are left with perfect plugs too. I'm using tape to cover my vent holes though...so you can only cover a small area if need be. I hope this makes sense! Good luck to ya!!