fan in incubator

If you’re looking to buy a new incubator, or maybe you’re just doing some research, you’ve probably come across still air and forced air incubators. The difference may seem small, so it can be confusing to make an educated decision between the two. Below is more information on the difference as well as why you should buy a forced air incubator. Please reach out to Brinsea, the Incubation Specialists, if you have any further questions! You can reach us by phone (888) 667-7009, or on Facebook and Instagram.

Still vs. Forced

Still air incubators are exactly what the name implies; they are incubators without a fan. The heat usually comes from above, which means the top portion of the incubator gets much hotter than where the eggs are. The temperature often needs to be set over 100°F in order to incubate eggs.

Adding a fan to the incubator changes the situation dramatically, since it eliminates the temperature variation from top to bottom. This is necessary for, say, a cabinet incubator where eggs are set on different levels. In this scenario it is important for the temperature to be uniform throughout the incubator.

If you are planning on incubating a small number of eggs that will all be on the same level, however, still vs. forced becomes a decision you have to make. We’ve already mentioned that fans eliminate the temperature gradient, but why else might you want a forced air incubator?

Relative Humidity

In a still air incubator, temperature variations can be quite extreme, sometimes with a 7°F difference between the top and bottom. This variation also causes a variation in the relative humidity, or RH, percentage. You can learn more about RH in our Humidity in Incubation article. RH is closely related to the temperature, which means that as the temperature goes up the RH goes down. So the RH will be lower near the top of the incubator, where the heater is, and higher near the eggs at the bottom of the incubator. This variation makes it difficult to properly measure both the temperature and RH, which can spell disaster during incubation.

Measuring Temp in Still Air

Of course, to get an accurate temperature and RH measurement, can’t you simply place the thermometer and hygrometer in with the eggs? Technically you can, but sensors placed around eggs and chicks can be exposed to damage and contamination. They also might not produce an accurate measurement due to the metabolic heat put off by the eggs. Therefore, measuring temp and humidity in a still air incubator has to be done above the eggs, and then the gradient has to be taken into account. 

The ambient conditions need to be taken into account as well, because if the outside air gets colder then the eggs will get colder as well. In situations like this the temperature in the incubator will need to be increased to keep the eggs in the ideal range. 

The Ease of a Forced Air Incubator

Any complications that come with a still air incubator can be eliminated by simply fitting a fan. The environment will be more predictable and there will be less variations to take into consideration. Temperature and RH will, ideally, be uniform throughout the incubator so you can measure and verify at almost any point. So why would anyone ever consider a still air incubator?

Why Buy Still Air?

In the end it is up to personal preference, but generally speaking still air incubators are less expensive than forced air incubators. They can be close to the same price, however, depending on the brand, because still air incubators usually need more insulation than forced air. 

A temperature gradient that can be found in a still air incubator might more closely replicate conditions found in the wild, so an argument can sometimes be made that still air is better due to this fact. There is no real conclusive data, however, although studies have been done with still air vs. forced air and the still air incubators are more likely to have successful hatch rates. 


Most avian species need to be kept in a temperature range of 98.6 - 100.4°F, with 99.5°F usually being the ideal. Waterfowl should be kept in the same range, but with 99.5°F being the max temperature. In forced air incubators this is relatively simple to measure, but still air incubators can be tricky. The temperature reading will depend on where the thermometer is, so adjusting the height will cause the reading to change. Still air incubators should come with instructions on what to set the temp to based on what the thermometer shows at a certain height. 


In a forced air incubator the humidity needs to be around 60-65% during hatching. Again, this is a relatively easy thing to measure in forced air. Low humidity will dry out the membranes and prevent chicks from hatching, and humidity that is too high will drown the chicks. Still air incubators typically don’t have as much of a problem with low humidity, and in both types of incubators the humidity will naturally spike as the first chick emerges. However, measuring the humidity in a still air incubator is difficult, so that should be taken into consideration.


Technological advances are making it possible to be more precise with incubation techniques while also reducing the cost of such incubators. More research and experimentation needs to be done to properly determine whether forced air is better over still air or vice versa. 

Some research has suggested that eggs incubated naturally under their parents for the few first days and then transferred to an electric incubator hatch at higher rates than eggs incubated in an electric incubator from the start. 

Eggs under still air incubators also seem to be more tolerant of temperature and humidity deviations than eggs in forced air incubators. Forced air incubators are sometimes perceived as the new and improved version of incubators, but it seems more research needs to be done into the process before this claim can accurately be made.

Contact Us

For more information on still air vs. forced air, or if you have any questions about our products, feel free to reach out to Brinsea Products by phone or on social media. You can call us at (888) 667-7009 or message us on Facebook and Instagram. Happy hatching!