Air in the chamber must be well mixed in order to accurately measure the CO2 concentration in the chamber.
Fans are not ideal to mix the air because they create high turbulence and cause large pressure gradients inside the chamber. Experiments show that a fan oriented toward the soil can pressurize the soil and suppress the CO2 flux; a fan pointed away from the soil causes the opposite will happen. Generally, the turbulence created by a fan is higher than desirable.
The LI-8100A eliminates the need for a fan with the following characteristics: