10-inch round, universal make-up air damper kit for use with any Zephyr range hood motor operating over 300 CFM and up to 1,200 CFM. When range hoods exhaust air out of your home, negative air pressure is created unless the exhausted air is replaced by fresh outdoor air. Zephyr’s make-up air damper is designed to balance the air pressure in your home by automatically opening to allow fresh air in while the range hood is operating.