With careful management, foster hens will produce excellent hatches. The hen can be left to hatch the eggs herself, or they can be transferred to an incubator for the last few days. If the hen hatches them herself she can also be allowed to brood the chicks, or they can be artificially brooded. Incubators are designed to simulate the environment underneath a hen. Whether the incubator will hold four eggs or forty thousand, it must be able to supply, either by itself or with your help, heat, humidity, air circulation, and turning.
Heat is produced by a heat element and is regulated by a thermostat.
Thermostats are either the wafer type or an electric thermostat, which is more accurate and reliable. A backup thermostat should be included to keep the eggs from getting too hot if the main thermostat fails. Eggs should be incubated at 99.5-99.75 degrees Fahrenheit. A couple days before the eggs are due to hatch, the temperature should be dropped around a degree because the chicks in the eggs are producing heat on their own. Putting pans of water in the incubator controls humidity and adjusting the surface area of the water to control the rate of evaporation or adjusting vents in the incubator to control the rate humidity escapes.