HUMIDITY DURING INCUBATION
HUMIDITY MANAGEMENT DURING INCUBATION - The ROLE
A chicken transfers heat by skin contact. An incubator must do it by air and moist air does it better than dry air.
You'll hear advice that while incubating, humidity is not as important as temperature which can lead to carelessness.
While incubating, there needs to be humidity enough to have effective heat transfers to and then from the eggshell to the air, minimum 40%, but not so much humidity averaged over the 19 days such that it prevents enough evaporation resulting in too small an air cell. We can't say this often enough.
Temperature's role is well understood, whereas the role of humidity is less so, making it `the villain' whenever things go awry and we don't understand why.