Because homes today are built more tightly for better efficiency, it has become crucial to provide replacement (Make-Up) Air when operating range hoods. Make-Up Air prevents the ill effects from negative pressure within the home, such as smoke backing up in the range hood. Throughout the country, there are codes that require Make-Up Air if the range hood exhausts more than 300 or 400 CFM. The newest standards require the Make-Up Air Damper to be interlocked to the range hood so the operation is synchronized. The damper opens and closes as the hood is turned ON and OFF to provide the most energy efficient method. Only BROAN offers this feature, which is built in to several range hood models.