WHAT'S THE CORRECT HUMIDITY FOR HATCHING CHICKEN EGGS?

Incubator humidity is one of the most talked about points in incubation and chicken keeping. It's open to a great deal of debate, resulting in many anxious nights for first timers and experienced breeders alike.

The first rule of incubation humidity: Don't panic!

Unlike temperature - which needs to be kept constant - humidity can vary greatly without having any adverse effect on your hatch. Guidelines suggest an average humidity level of 45-55%. But in reality, keeping within such a tight range is almost impossible. Incubators equipped with automatic humidity control, such as the Rcom King Suro Max 20 incubator, or others, allow and facilitate humidity control in the hatching of eggs.

What does it mean when we say, "Relative Humidity"?

A Incubator humidity is a moving target. By this I mean that it depends on two factors: air temperature and air pressure.

If you imagine that the air around us is a giant sponge, you could imagine that it has a certain, critical capacity at which it's "full" with evaporated water and cannot hold any more. Let's call this, 100% humidity. If it begins to rain, and the air loses half its moisture, it could be said to reduce to 50% humidity.

However, in reality air is different to a sponge, because hot air can hold more water than cold air. That's why hot countries tend to feel more humid than cold countries - there is more water held in the air. So 100% humidity at 37,5°C means there is a lot more water in the air than 100% humidity at 10°C. Ever wondered why carpets get damp in the cold basement? There's your answer. The cold air in the basement cannot hold as much water as the warm air upstairs, so the basement carpets get damp instead.

A similar principle applies with air pressure too. But unless you're planning to place your incubator on Mount Everest, it's not likely to concern us too much.

So, in summary, "relative" humidity is exactly that… it's the amount of water that's in the air, as a percentage of the maximum amount of water that the air could hold at its current temperature. Usually expressed as RH%.

Should the humidity rise during hatching?

In general terms, it's good practice to increase humidity for the hatching period (days 18-21 of incubation). A figure of 65-70% relative humidity is a good target to have in mind. Higher humidity during the final three days of chicken incubation helps to soften the egg shells, making the hatch a less tiresome experience for the hatchlings.

Again, for the hatching period, incubators with automatic humidity control facilitate and are crucial in the process of humidity control to ensure more and better hatchability rates as well as chick quality for the newly hatched chicks.

Incubators that do not have automatic humidity control, rely on having several separate reservoirs for the water. Having more than one helps regulate evaporation, as water can only evaporate from the surface. The more there are the greater the evaporation surface area, resulting in a higher humidity level when all the reservoirs are being used. See some examples below.

The Rcom 10 Pro has a circular humidity pot in the base of the incubator. The pot is split into two, allowing you to double or halve the surface area of water for greater control of humidity levels. Similarly, the FIEM Cosmo Digital incubator features eight modular humidification basins in the base of the incubator. You can just fill one basin, or fill all them, depending on how much evaporation you want.

And finally… less is better!

When it comes to chicken egg incubation, the No.1 mistake made by first time breeders is too much humidity. It's vitally important to remember that embryos need air, not just moisture. Too much humidity will effectively suffocate the embryos and not allow them to grow fully inside the shells. So, when considering whether to add more water to the incubator, follow this simple rule… If in doubt, keep water out!