To ensure accurate thermal results, we installed the same hardware in each case in virtually the same way. Components included the Asrock Fatal1ty 990FX Professional, Phenom II X6 1100T, Prolimatech Megahalems in passive mode (i.e. no fan actively dispelling heat), Inno3D GeForce GTX 580 OC, two Western Digital Scorpio Blue hard drives, and OCZ's ZX 1000w power supply.
Out of the box, the HAF XB wasn't overly impressive. In fact, it ranked similarly to the Scout 2, which comes with just a single 120mm fan. The processor hit a warm 50 degrees at idle while the graphics card sat at 40 degrees. Adding in a Silverstone AP121 (1500 RPM) 120mm fan to the rear of the case reduced the processor idle temperature by 16% down to 42 degrees. This made the HAF XB comparable to the Enforcer.
Under load, the HAF XB suffers without an exhaust fan as processor temperatures reach 96 degrees. Adding an exhaust reduced the temperature 11% to 85 degrees -- below the Enforcer, but still far off from full towers like the HAF X.