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Humidity in Incubation: A Comprehensive Guide
Of the four critical factors in incubation—temperature, ventilation, turning, and humidity—humidity is often the most misunderstood and difficult to control. Conflicting advice is common, but getting it right is essential for a successful hatch. This guide from the Incubation Specialists at Brinsea will clarify what you need to know.
Key Takeaways
- The Goal is Weight Loss: The primary purpose of humidity control is to ensure eggs lose 13-15% of their initial weight by hatch day.
- High Humidity is More Dangerous: Too much humidity prevents adequate weight loss, leading to a small air sac and a high risk of the chick drowning or being unable to pip.
- Increase Humidity for Hatching: During the last 2-3 days (lockdown), humidity must be raised to at least 60% RH to keep the membrane soft and prevent "shrink-wrapping."
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The Core Principle: Why Humidity Matters
Eggshells are porous, allowing moisture to escape throughout incubation. This process is essential for creating a large enough air sac inside the egg, which the chick uses to take its first breaths. The main goal of humidity control is to ensure the egg loses an ideal amount of weight (13-15%) from setting to hatching. This provides the chick with the perfect balance of space to breathe and move.
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The Dangers of Imbalance
If Humidity is Too Low If Humidity is Too High - Causes excessive weight loss.
- Creates an overly large air space.
- Results in a smaller, weaker chick.
- Chick may be unable to hatch on its own.
- Typically less of a problem than high humidity.
- Prevents sufficient weight loss.
- Results in a small, inadequate air space.
- Can cause respiratory problems for the chick.
- Makes it difficult for the chick to maneuver and hatch.
- Chick may drown or die from weakness.
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The Most Reliable Method: Weighing Eggs
If you don’t have a reliable hygrometer, weighing eggs is the best way to track progress. Most bird species (except the ostrich family) need to lose 13-15% of their weight from day 1 to hatch day.
1. Weigh & Plot: Weigh eggs on Day 0 and plot the starting point on a graph.2. Calculate Target: Calculate the target final weight (Start Weight x 0.87).3. Draw the Line: Draw a straight line on your graph from the start weight to the target end weight.4. Track Progress: Weigh the eggs every few days and plot their actual weight.5. Adjust: If the actual weight is above the line (not enough loss), decrease humidity. If it's below the line (too much loss), increase humidity.
A Note on Hygrometers: Cheap hygrometers that can't be calibrated are risky. You get what you pay for! Expensive, reliable hygrometers need frequent calibration. All Brinsea incubators can be calibrated. -
How to Adjust Humidity
1. Water Surface Area: The more water surface area, the higher the humidity. All Brinsea incubators have two water pots/channels for flexibility. The depth of water does not matter. For very high humidity, our EX units come with evaporating pads (also available for purchase).
2. Ventilation: More fresh air reduces humidity. To increase humidity, reduce the ventilation (but never block all holes, as chicks need oxygen).
Ambient Humidity: Your room's humidity affects the incubator. A dry room in winter requires different settings than a humid room in summer. -
Common Questions & Special Cases
Should I spray my eggs with water?
We do not recommend this. It only raises humidity for a short time and can cause thermal shock if the water is too cold.
Why isn't my humidity pump working?
Brinsea incubators with automatic humidity pumps are designed not to pump if the temperature is too low. Let the incubator reach 99.5°F first before calling for service.
What about automatic humidity management?
Brinsea EX models come with a humidity pump and internal hygrometer, making incubation less stressful. You set the desired RH%, and the pump adds water as needed. Evaporating blocks can be added to help maintain stability during hatching.
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The Final Stage: Lockdown & Hatching
For the last 2-3 days ("lockdown"), humidity must be raised to at least 60% RH. This is critical to keep the inner membrane soft. If the membrane dries out, it becomes tough and traps the chick, a condition called "shrink-wrapping." Raising humidity at the end will not significantly affect the total weight loss if it was correct beforehand.
Do not lift the incubator lid after the first chick hatches! This causes a sudden humidity drop, which can shrink-wrap the remaining chicks.
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Advanced Details: The Science of Humidity
Relative Humidity (RH%): RH% measures water vapor in the air compared to the maximum amount the air could hold at that specific temperature. This is why 50% RH at 70°F is different from 50% RH at 90°F. As temperature increases, the air's capacity to hold water increases. So, raising the incubator's temperature without adding water will cause the RH% to drop.
Wet Bulb Temperature: This is another way to measure humidity, done by checking the temperature of a thermometer with a moist wick around its bulb. As water evaporates from the wick, it cools the bulb. The difference between this "wet bulb" temperature and a regular "dry bulb" temperature can be used to calculate RH%. The two temperatures will only be the same at 100% RH (or if the wick dries out). This method is very difficult to use accurately in a still air incubator.
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Brinsea Auto Humidity Control Incubators
Fully automatic incubator with integrated humidity control for a stress-free hatch.