There are three major ways that ventilation systems create noise. First, the fans and other mechanical equipment can create vibration and noise as they operate. Second, air moving through ductwork creates noise and vibration. Third, for ventilation systems to bring fresh air into the home, there must be air intake grilles on the home's exterior. These grilles not only bring in air, but also noise from the outside, including traffic and pedestrian noises, wind and background noise.
Fortunately, all of these sources easily can be controlled using relatively simple acoustical techniques. To minimize noise from fans, choose Quiet Fans, which are available from almost any fan manufacturer. These models operate between 10 and 20 dBs on average [source: Bower], which is no louder than a whisper between two friends [source: Truax] Designed with smaller, more efficient motors, these fans operate at surprisingly low energy levels while moving tremendous amounts of air. They're tightly constructed to minimize rattling and vibration and often can be installed with the motor in a separate compartment from the fan itself, allowing the fan to move air within a living space while the motor operates behind the scenes.
To keep vibration and air noises quiet, choose ventilation ducts that are lined with insulation. According to ASHRAE (the American Society of Heating, Refrigeration and Air Conditioning Engineers), a bare ventilation duct has a sound absorption coefficient of 0.05, meaning that 5 percent of sound that comes into contact with the material is absorbed. Duct lined with 1inch (25.4 mm) of insulation, however, has a sound absorption coefficient of 0.68 [source: Dolgin].
Use the largest duct that can fit into an available space to slow down airflow, further reducing noise. Also, minimize the number of duct bends and elbows and seal all joints using duct mastic to keep air flowing properly and prevent whistling or whooshing noises from ducts.
To keep noise from entering the house through fresh air intake units, choose grilles specifically designed for acoustic ventilation solutions. These grilles are lined with insulation and modified to include sound dampers that keep noise from entering the home. Be sure to locate these grilles away from the street and from other noise sources for maximum impact.