How to Increase or Lower Incubator Humidity

The target numbers

For chicken eggs: 45–55 % from day 1 to 18, then 65–75 % from lockdown (day 18) until the hatch is over. So 70 % is right at lockdown but too high in the first 18 days. Other species are in the temperature and humidity guide.

How to increase humidity

• Fill more water channels or trays; humidity depends on the water surface area, not the depth.
• Put a clean, damp sponge or cloth in the water tray to add surface.
• Top up with warm water so the temperature does not drop.
• Partly close the vents, but never close them fully during hatching, when chicks need air.
• Keep the door shut; every opening lets humid air out.

How to lower humidity

• Remove some water or cover part of the tray to reduce the surface area.
• Open the vents a little more.
• Move the incubator out of a damp room: in coastal KwaZulu-Natal and the Western Cape winter, room humidity alone can push the incubator high. A dehumidified or air-conditioned room helps.
• Some farmers in humid areas run a “dry hatch” with little or no water until lockdown, watching the air cell size.

Check it with the air cell, not only the display

Candle the eggs on day 7, 14 and 18 and look at the air cell at the blunt end. It should grow steadily until it takes up roughly a third of the egg by day 18. A small air cell means humidity is too high; a very large one means too low. Also check the display against a calibrated hygrometer. See candling eggs.