Normally we pick fan CFM to be allow of balance of heat vs air quality control. The problem is airflow that recirculates every few minutes isn’t always evident without smoke trails. If you just put your hand up to the door or an air intake you can’t feel anything. Plus, not every customer cares about printing high temperature filament like ASA or nylon.
For the maximum air quality control we've designed new 120mm fan adapters. This not only gives a more satisfying feel of moving air, but the more powerful fans typically come with speed control. (Note that we don’t actually sell these fans, as you can get them as cheap as we can from Amazon.) This new larger fan is featured on the upcoming release of a Qidi X-Pro enclosure specifically designed for high air flow for maximum air quality control.
The fan can either be mounted right on the enclosure OR close to an outside window vent. The hose can either be 3 inches or 4 inches. The smaller hose is usually just fine as it’s plenty large for the volume of air, but the 4 inch is much more likely to be found at your local hardware store since it’s the standard size for a clothes dryer.
Here's what the 120mm fan looks like when mounted on an enclosure:
Because the larger fan can be pretty clunky when mounted right on an enclosure, here’s one typical configuration where the fan is mounted close to a window.