The quiet vent fans are very similar to other bathroom ventilation fans except for the fact that they are designed to run quietly. In general, a silent option comes with higher-end motors, which are much more efficient than their older counterparts that significantly decrease the noise level. The motor may be an ECM controlled motor or brushless DC motor. Brushless motor is one that affects the sound level of a fan. Models with brushless motor are silent while running as there are no brushes to rub against other parts of the fan. As long as the motor itself is quiet, the fan will run silently. Additionally, most of the models of silent vent fan come with 4-inch or 6-inch vent hose rather than the standard 3-inch duct. Larger size vent pipe can ventilate more air with less energy consumption. It also helps to reduce the noise level dramatically.