Suncourt Inductor Inline Duct Fan, 4 Inch Diameter, Indoor Air Ventilation IMPROVED AIR CIRCULATION - Have rooms that are too warm or too cold? These inline duct fans will aid in boosting airflow to selected areas. EXTEND CURRENT APPLIANCES REACH - Installing these in-line inductors will help your existing furnace or air conditioning unit get to those hard to reach rooms. ENERGY EFFICIENT - Enjoying improved home air quality doesn't have to cost and arm and a leg. Most units operate on an economically low wattage. FLEXIBLE OR METAL DUCTS - The housing of the inductor is galvanized metal which makes it compatible with most systems. Whether flexible or metal ducts, it will work with your air delivery system. QUIET, YET POWERFUL - For maximum performance and minimum noise, the best location to install these fans is 6-10 feet from the register needing boosted air.