Incubator temperature and humidity: settings and checks

Temperature and humidity are connected, but they are not controlled in the same way. Temperature must remain stable around the setting appropriate for the machine. Humidity mainly controls how quickly the egg loses water during the 21 days.

This guide covers chicken eggs. For another species, use a species-specific programme and the manufacturer’s manual.

Starting settings

Incubator type	Days 1–18	Days 19–21	Important point
Forced-air, with fan	About 37.5–37.8 °C; 58–60% RH as a starting point	Temperature per manual; at least 65% RH as a starting point	Air should circulate without blowing directly on the eggs
Still-air, without fan	About 38.9 °C measured at the top of the eggs	Follow the model manual	Temperature varies strongly from top to bottom

These values are starting references, not a universal guarantee. Sensor accuracy, altitude, climate, shell characteristics and incubator design can all change the useful setting.

Measure in the right place

In a still-air machine, position the thermometer at the top level of the eggs without touching the shell. In a forced-air machine, make sure the sensor is not against a cold wall, above the heater or directly in the fan stream.

Compare the display with a reliable thermometer before the cycle. Run the empty machine for several hours, then check several tray positions. A stable setpoint with large differences between zones suggests an airflow or loading problem.

Adjust temperature without creating swings

Do not correct every brief fluctuation. Opening the lid, adding water and manual turning temporarily lower the reading. Wait for the machine to settle before changing the setpoint.

Prolonged high temperature can bring hatch forward and increase embryo loss.
Prolonged low temperature can delay hatch and produce weak chicks.
If temperature repeatedly rises and falls, inspect the sensor, fan, relay, room position and power stability.

Change one parameter at a time and record the time, previous value and new value.

Understand humidity

Humidity does not depend only on the volume of water. It depends mainly on the exposed water surface, ventilation and room humidity.

To raise humidity, gradually increase the water surface or use the system specified by the manufacturer.
To lower it, reduce the water surface without closing required ventilation openings.
Clean water channels because deposits can reduce evaporation or distort readings.

Never seal vents to retain humidity. The embryo takes in oxygen and releases carbon dioxide through the shell, especially near hatch.

Use the air cell as a check

During candling, the air cell should grow gradually. If it remains very small, moisture loss may be too low; if it becomes very large too early, moisture loss may be excessive. Compare eggs from the same source and look for trends across several cycles.

A more precise method is to weigh a sample of eggs at setting and at regular intervals. It requires a reliable scale and a target appropriate for the flock; do not improvise it halfway through a cycle.

The final three days

From day 18, stop turning, place eggs in hatch position and raise humidity according to the manual. Open the incubator as little as possible: a rapid humidity drop after pipping begins can dry the membranes.

Keep the designed vents open. High humidity must not be achieved at the cost of insufficient fresh air.

Daily control sheet

Check	What to record
Morning and evening	Temperature, humidity and room temperature
After an alarm	Duration, highest or lowest value, action taken
At candling	Development, air cell, clear or stopped eggs
At hatch	First and last chick, number hatched, observed abnormalities

Records from a full cycle are more useful than a correction based on one egg. Also read the complete 21-day guide and the low hatch-rate diagnostic method.