Yes, an air admittance valve (AAV) can be installed in an attic. However, there are several considerations that must be taken into account:
• Ventilation is essential to the proper functioning of the AAV and should not be obstructed by insulation or other materials.
• The AAV should be mounted with its opening facing downwards to prevent backflow of sewer gases into the house.
• It should also have at least 6 inches of clearance from any combustible material and a minimum distance of 3 feet away from any electrical wiring.
• Finally, it's important to adhere to local codes and regulations when installing an AAV in your attic.
Overall, if these considerations are taken into account then installing an AAV in your attic is perfectly safe and acceptable.