The Covid pandemic has made us aware of the need to improve air quality. This is why heating, ventilation and air conditioning (HVAC) are important in buildings to protect people’s health. While this equipment ensures air quality by evacuating polluted air and bringing in fresh air, it can allow a pollutant to enter: noise. Noise can have harmful effects on humans such as sleep disorders, cognitive problems or even an influence on cardiovascular diseases. Recent developments in the acoustic field have shown the use of metamaterials capable of reducing noise while maintaining good ventilation. The solution proposed here is based on sonic crystals arranged in a certain pattern, following Bragg’s law. This pattern of sonic crystals is known as acoustic metacage. The metacage can be tuned to reduce noise over a wide frequency band. Here it is integrated into the design of an air vent. This design is optimized using open-source numerical simulation programs. The goal of the optimization is to determine the ideal metacage configuration that reduces both transmitted noise and ventilation loss. After optimization, a metacage prototype was 3D printed for laboratory validation. A good correlation was obtained between the measurements and the simulations. The optimal result showed third octave bands with maximum sound transmission loss (STL) greater than 10 dB, with an average of 3 dB for all other bands up to 10 kHz. This gain in STL did not come at the expense of ventilation efficiency by adding this metacage to the design of the air vent.