As mentioned earlier, a denser chassis results in high fan noise. In a similar vein, shown here is a fan PQ curve, with the power draw curve superimposed. The power draw in Watts shown on a fan catalog spec is for free air conditions. When a fan is under load, the power draw can increase significantly, as shown in the green power curve. The black system impedance curve, as compared to the blue system impedance curve, shows a higher power draw. To reduce fan power draw, a designer can reduce the density of the chassis.