How Does an Egg Incubator Work?

The principle

A fertile egg needs three things for 21 days (for chickens): steady warmth of about 37.5 °C, the right humidity so it loses the right amount of water, and regular turning so the embryo does not stick to the shell. Fresh air matters too, because the embryo breathes through the shell. An incubator provides all four in a controlled box.

The parts of an incubator

• Cabinet. An insulated box that keeps heat in and outside temperature swings out.
• Heating element. Makes the heat. Small incubators use a heater wire or element; older and homemade ones use light bulbs.
• Temperature controller (thermostat). Reads a temperature sensor and switches the heater on and off to hold the set point. Digital controllers are far more stable than the old wafer thermostats.
• Fan. Moves warm air around every egg so all trays sit at the same temperature. See forced air vs still air.
• Egg turner and motor. A slow motor tilts the egg trays on a timer, usually every hour or two.
• Humidity system. Water trays or channels give off moisture; a humidity sensor shows the level, and some machines control it automatically.
• Vents. Let carbon dioxide out and fresh air in.

How the parts work together

The controller compares the sensor reading to the set temperature. When it is too cool, it switches on the heater; the fan spreads the heat; when the set point is reached, the heater switches off. The heater cycles on and off all day, which is why an incubator uses much less power than its heater rating suggests (see incubator electricity usage). Meanwhile the turner tilts the trays, and water evaporates to hold humidity.

When a part fails

• Temperature climbing: controller or relay stuck on. Unplug and cool the eggs, then call for support.
• Temperature dropping: heater, fuse or power supply. Check the plug and power first.
• Uneven hatch across trays: often a slow or dirty fan.
• Eggs not tilting: turning motor or its timer.

Own an IncubatorPro machine? Contact us for help under our warranty and after-sales support. Always check readings with a separate thermometer and hygrometer.