There is a lot of controversy out there regarding dry incubation. Here is my opinion, based on personal experience. Dry incubation is inconsistent, and therefore not recommended, and here is why.

Successfully incubating embryos requires stable conditions--stable humidity and stable temperatures. The temperature is kept stable by the heater, fan, and thermostat. Humidity, on the other hand, is only controlled by the equal evaporation of water in the incubator. When you dry incubate, you do not add any water, so the humidity in the incubator is whatever the ambient humidity is in the room. The problem arises when various weather fronts move through, that change the ambient humidity. Even taking a shower can change the ambient humidity in areas of your home, and depending on where the incubator is located in the house, this then in turn, changes the humidity in the incubator. There is no buffer. Humidity will change suddenly and this will affect the developing embryo. If you are lucky, and the weather says stable for the entire incubation period, with no weather fronts moving through, your dry hatch will be a success. But more than likely, a weather front will move through, and you will have a disastrous hatch, with very few or no chicks hatching, with crooked toes on the chicks, with chicks that suffer from spraddle legs. It is not the lack of water that causes this, but rather the constant up and down change in humidity.

If you think logically, a hen sitting on eggs controls both temperature and humidity by the simple act of covering the eggs with her own body, insulating them from any changes in outdoor temperature and humidity. When we artificially incubate eggs, we have to create similar conditions if we are to be successful.