I have one at either end of my styrofoam cooler, about nickle size, 3 " from bottom. Just high enough nothing will block them. I also have a larger one on top. Thats the one I block when I raise the humidity. I have never blocked the bottom ones. I'm not sure what your incubator looks like but I liked mine much better afer I bought a super cheapo picture frame from the dollar store and used the glass to make a window in the cooler. It's about 6" x 10". I put mine on the top but now I'm thinking maybe it would have been more fun to watch from the front side.Ok, I just had a HUGE DUUUUUH moment. I am working with a homemade foam cooler incubator. I was doing some MORE reading on the internet before I pick up my eggs, just making sure I'm prepared as I can be. As I'm reading it dawned on me, I have ZERO ventilation in my bator. ZERO. I'm guessing this is a VERY bad thing. So do I cut small holes around the bottom (maybe 2 ) and one in the top? Keep the pieces so I can plug them as needed and for lockdown, right? I feel like such a dummy right now. I really don't know how I overlooked this and it likely cost me my last hatch.