I personally think dry incubation should be used with still air models only. I have both types and the water evaporation on the still air versus fan model is VERY different. In my still airs, the water can last the entire 21 days without a refill. In the fan models the air can TOTALLY evaporate in 3 or 4 days. So, basically what is happening is the eggs are in a dehydrator, sapping out moisture, regardless of what the hygro says.