humidity in incubation

If you’ve ever incubated before (or even if you haven’t), you probably know that there are a lot of variables you need to keep track of. There are four primary factors to consider when incubating -- temperature, ventilation, turning, and humidity. Out of the four humidity is the most difficult factor to control and sometimes measure, which is why it is commonly misunderstood. If you’ve noticed the conflicting information on the internet about humidity, you’ve come to the right place. The Incubation Specialists at Brinsea are here to answer your questions! 

Check the Basics

Our incubators that feature automatic humidity pumps are designed not to pump if the temperature is too low. So if you’ve just plugged your incubator in and can’t figure out why the pump isn’t working, check to see if it’s reached 99.5°F. If it hasn’t, give it some time to get up to temp before you give us a call. 

What Does Humidity Do? 

Egg shells may look solid, but they are actually porous. You can test whether a supermarket egg is good to eat by floating it in water. Fresher eggs will sink because they weigh more, while old eggs will float because they have much more empty space in them. This is also true of eggs you are trying to incubate, although we don’t recommend a float test for those eggs. 

While eggs are incubating they will naturally lose weight. It is important to have your humidity set to the right percentage so that your eggs are losing an ideal amount of weight. If the humidity is kept at the right level, developing chicks will be able to use the available air space to breathe and move around.

If Humidity is Too Low

Low humidity will cause the eggs to lose too much weight, which means the air space will be larger than what is ideal. A large air space also means the chick will be smaller than normal. Small chicks are weak chicks, and weak chicks cannot always hatch on their own, and they may die just before or just after hatching. 

It should be noted, however, that low humidity is typically less of a problem than high humidity, which we will cover next.

If Humidity is Too High

If low humidity equals too much weight loss, then high humidity equals not enough weight loss. In this case the air space will be smaller than normal, and the chick will be larger. A large chick may be a strong chick, but a small air space can affect the respiration and cause problems that way. This also causes a lack of space, making it difficult for the chick to move around and break out of the shell.

Once a chick has pipped in a shell that hasn’t lost enough weight they can die due to weakness from lack of air, or because they cannot maneuver to break out the rest of the way. 

How Do You Measure Humidity?

Now that you know the dangers of incorrect humidity, let’s dig into how to measure it. We want to mention that unlike temperature, humidity is not a strict variable. If the temperature fluctuates even a small amount it can spell disaster, but humidity is more of an average variable. High humidity at the beginning of incubation can be corrected later on with lower humidity and vice versa. 

Humidity is calculated by measuring the water vapor in the air. One of the easiest ways to measure the water vapor is by figuring out the Relative Humidity percentage, also known as RH%. The other way is with a Wet Bulb, and we explain both methods below. 

Relative Humidity or RH%

When you see the RH% on our incubators, for example, you are seeing the measurement of water vapor in the air compared with the maximum that could be absorbed at that temperature. Let’s put emphasis on the fact that RH% is based on the temperature of the air. 50% humidity at 70°F is different from 50% humidity at 90°F. 

Maximum possible water vapor capacity increases as the temperature increases, so raising the temperature in an incubator without adding water will cause the RH% to drop. When you’re checking your incubator humidity, therefore, it is very important to also note the temperature. It is also important to take the temp into consideration when checking your ambient humidity.

Wet Bulb Temperature

This is a different way to measure the humidity, and it is done by checking the temperature of a thermometer with a moist cotton wick around its bulb. As the water from the wick evaporates it cools the bulb, which is similar to what happens when you step out of the shower into a cool bathroom. 

The Wet Bulb technique can be used as a cheap way to measure the RH%, which is done by taking the difference between the Wet Bulb and Dry Bulb temperatures. There are only two instances where the WB and the DB temperatures would be the same -- when the air has absorbed all the water it can (100% RH), and when the wet wick has dried out! It should be noted that it is very difficult to measure the WB in a still air incubator. 

How to Achieve the Correct Humidity Levels

So what happens if you don’t have a hygrometer, or you aren’t sure if your hygrometer is accurate? As we mentioned above, humidity that is too high or too low will affect the weight loss of the egg during incubation. So, in theory, you could simply weigh the eggs periodically to check on their progress? If you’re hatching in an incubator without a reliable hygrometer then that is exactly what we recommend doing. 

Most bird species (with the exception of the ostrich family) will need to lose between 13 and 15% of their weight from the first day of incubation to the day they hatch. By weighing the eggs every few days you can accurately adjust the humidity to compensate for too much or too little weight loss. 

If you’re good at math it may be fairly simple for you, but for those of you that aren’t it may be helpful to draw a graph (see below) to keep track. The incubation days will be our x-axis going across, and the weight will be the y-axis going up. You can plot out the ideal weight loss from day 0 through to hatching, which we show here in dark blue. Then every few days when you weigh the eggs, mark their weight along the graph and note where it falls on the blue line. We’ve done that here with the pink dots.


You Get What You Pay For

Cheap hygrometers can easily tell you what the RH% is, but how accurate are they? We will tell you right now that if it is cheap and can’t be calibrated, you get what you pay for! Some can be accurate but it just isn’t worth the risk. 

Expensive hygrometers are much more reliable but they need to be calibrated frequently to ensure they are reading properly. All of our incubators can be calibrated, so even if the accuracy does come into question that can be fixed with a simple phone call to our service department.

Altering the Humidity During Incubation

There are two controllable factors to consider when altering the humidity during incubation. The first is water surface area. The more water surface area there is inside the incubator, the higher the humidity will be. Depth of water does not matter for humidity, other than to maintain it. The second controllable factor is how much fresh air the incubator is able to draw in from the outside. 

All Brinsea incubators have two water pots or channels to give the user more flexibility when it comes to water surface area and evaporation rates. In order to increase the humidity all you need to do is put water in both channels and reduce the ventilation. Never block off all of the holes in the incubator as the chicks do still require oxygen to breathe. 

What happens if you’ve put water in both water channels and still cannot achieve the correct humidity level? Our EX units come supplied with evaporating pads or blocks that can help to raise the humidity. They are also available for purchase in our Consumables section.

Ambient Humidity

Due to the fact that our incubators are not air-tight, the ambient humidity will have an affect on the humidity inside the incubator. Whether or not there is a humidifier or dehumidifier in the room, if you are running the heater, if you turned the A/C off and opened the windows, etc., these are all factors that could cause the humidity in the incubator to fluctuate. Due to this, it is usually impossible to use the same method for humidity in the summer that you did in the winter. Houses tend to be dryer during the winter and more humid during the summer, but that also depends on your local area. 

Should I Spray My Eggs with Water?

This is a fairly common practice that is intended to raise the humidity in the incubator, but it is not something that we recommend. The humidity will only be raised a short time before the small water droplets on the eggs evaporate, so it is not an effective solution to low humidity. It is also not recommended due to the fact that the water could be a much lower temperature than the eggs, which can cause issues as well. 

Humidity During Hatching

For virtually all birds, humidity needs to be higher at hatching than it was throughout incubation. We recommend raising the humidity during “lockdown,” or, the last few days of incubation. If you have been weighing your eggs then the weight loss should be right around 13-15%, and raising the humidity at the end will not significantly affect this. 

High humidity is necessary because of the membrane that the chicks must break through in order to hatch. If the membrane is allowed to dry out (due to low humidity), then it becomes too tough for the chicks to tear. They are then unable to hatch, and this is what is known as shrink wrapping. 

During hatching the humidity should be at least 60% RH, and in order to keep the humidity stable it is recommended to keep the lid on the incubator at all times. If the lid is lifted after a chick has hatched the humidity will immediately drop which could cause other chicks to become shrink wrapped.

Automatic Humidity Management

As mentioned above, our EX models come equipped with a humidity pump and internal hygrometer that make incubation a little less stressful. Similar to the temperature control, the user can adjust the humidity level on the incubator and the pump will take care of adding water as necessary. For hatching the humidity level can be increased and evaporating blocks can be added as necessary to help maintain stability. 

Contact Us

If you have any questions about your incubator or anything mentioned in this article please feel free to contact us! We are available by phone (888) 667-7009 or on Facebook and Instagram. Happy hatching!