Review on Noctua NF A4X20 FLX Premium 40X20Mm by Chris Palmer

I have been using Noctua fans for many years and have never had a problem with any of their offerings. Although they are not the cheapest in the long run, they are durable and good for continuous operation (CO). There seems to be some confusion surrounding 40mm fans, partly due to the number of offerings from Noctua in the 40mm space and partly due to differences in 40mm fan types. This fan in particular (NF-A4x20 FLX ) is a higher pressure fan designed to force air into a case where air is difficult to move. It fits very well in something like a 1U rackmount case, where there's usually very little room for extra ventilation. Because this fan is designed for static pressure, with a large center hub and small blades, it loses some of the overall CFM for moving air volume compared to 40 x 10mm offerings with a more traditional blade style. However, the total amount of air moving in an enclosed space is likely to be higher with a 40 x 20mm fan due to increased static pressure. If you plan to use the fan in an enclosed space that is harder to "breathe", choose 40x20mm and don't look back. If you use it outdoors or unrestricted, 40x10mm with traditional blades will probably work better for you when it comes to total CFM airflow.