yes, I do have a fan. I calibrated one Sally and they were within 1 degree of each other . I need to know more on how much air or vent holes are needed. What wishing said yesterday about the tunnel effect makes sense to me. Its very thick walls with styrofoam in between. could be the air is getting lost in between the 2 panels ? Asked son if I could stick his cat in there to see if it could breath and he wouldnt let me.
I suppose the cat would fit!

Mine only has 5 holes altogether, one above the fan in the lid that I have fully open all the time and 4 in the base in each corner. There quite small too but I do find when chicks have hatched the dander/fluff does get blown out of the top vent hole so I'm presuming the air is drawn through the incubator.
A tunnel affect?