Cooling Design And Fans
NZXT's Phantom 820 uses a standard negative pressure cooling design, which we know from How To: Properly Plan And Pick Parts For An Air-Cooled PC, Part 2 is the best way to go for performance-oriented configurations. An optional interior fan with an adjustable angle can be added. The image below gives us a good overview:
140 mm Back Fan
The preinstalled rear exhaust fan is a weak point in this case's cooling subsystem. It's too loud. Even on the lowest speed setting, the noise is noticeable. We'd recommend replacing it right away.
Immediately after running our first noise benchmark, we replaced that rear cooler with a 120 mm Noiseblocker NB-eLoop S-Series B12-1 at 800 RPM, and connected it directly to one of the fan headers on our motherboard. We're happy with the way this combination of components sounds compared to the stock configuration.
200 mm Fan
The three preinstalled 200 mm fans are less bothersome than the rear exhaust fan, but only if you run them at their lowest speed setting. Anything above that is simply too distracting. We wouldn't blame you for switching the larger coolers out as well, except that fan replacement would be pushing your case upgrade up above the $300 mark.
The side fan is only really necessary if you have a couple of Radeon HD 7970s or similarly warm-running cards installed. We recommend getting rid of it otherwise.
The interior fan and its adjustable angle can be problematic if you're trying to use it with long, high-end graphics cards installed (particularly if you're using more than one). We can appreciate what NZXT is trying to do with directional cooling, but bear in mind that it won't work universally.