Use of Incubator - Prior to starting this project, review the instructions for using the incubator. Incubators are either still-air or forced-air (fan ventilated). Operating instructions and optimum temperatures will differ with the two.
Location of Incubator - Locate your incubator in a draft-free room with the room temperature constant between 70° to 75° F. Avoid drafts and excessive variations in temperature. Be certain that the machine sits level. Do NOT place the incubator near windows where it will be exposed to the direct rays of the sun, since this can cause a rise in the temperature that can kill the embryos.
Temperature - in forced-air machines, air temperature will be the same throughout the chamber and should be kept at 99.5°. Plug in incubator, add water and run for several hours to be certain it maintains temperature before adding the eggs. After adding the eggs, wait two or three hours to adjust temperature as it will take time for the eggs to warm through and maintain temperature. Overheating is more damaging than under-heating. Short cooling periods do not usually harm embryos, for eggs will still hatch after several hours exposure to temperatures as low as 50° F during the second week of incubation. Periods of low temperature will slow embryonic development and require a longer period of incubation.
Humidity - Each incubator has instructions as to how to maintain the correct moisture level. The ideal moisture level is about 50 to 55 percent relative humidity for the first 18 days and about 65 percent for the last three days. Some variation above or below the ideal level usually will not affect hatchabillity drastically. When refilling the water pan, use warm water (99° F). Hot or cold water will affect the temperature of the incubator too much. It isn't the volume of water, but the total surface area.
Ventilation - Proper room and incubator ventilation is very important during the incubation process. While the embryo is developing, oxygen enters the egg through the shell and carbon dioxide escapes in the same manner. As the chicks begin to hatch, it is essential that they receive an increasing supply of oxygen. This means that the air openings on top of the incubator need to be opened to increase the flow of air.
Length of Incubation - Chicken eggs require 21 days to hatch. The incubation period of other species of poultry varies. For example: duck eggs require 28 to 35 days depending on the species. To help insure your chick hatch while students are in the classroom, stagger the start of incubation over two days, by adding a few eggs to the incubator in the morning and evening of Tuesday and Wednesday or Wednesday and Thursday. This increases the hatching period, and if the eggs are a little fast or slow they are less likely to hatch during the weekend.