My incubator is a still air homemade (thick styrofoam, not a purchased one) that was built by my dad. It isn't sealed the greatest but does the job. Anyways, along with a little air flow through the seals, the lid doesn't fit perfectly just sort of sits on top. Then on top of that I have many vent holes about a half an inch in diameter. 4 on the top and 3 on each side and 3 on the back. None on the front. I've got a 40 watt bulb in there and it keeps it about 101-102 with the occasional spike. With my last batch (first time incubating) I had 10 eggs in there and 8 had pips, only one got out on it's own and just barely. The rest just made no progress, so eventually I helped them all, all were shrinkwrapped with only their beaks out of the membrane, the membrane was almost white and just completely stuck to them. Humidity was about 30-35% for the first 18 days and 65-70 the last 3. There is no fan or humidifier outside the incubator that would cause air flow, so what the heck, is ventilation the problem? Thanks for reading.