Although Chicago is known as the Windy City, it is in fact less windy than many other major American cities. Average wind speeds range from 8 miles per hour (13 km/h) in late summer to 12 miles per hour (19 km/h) in spring months.
A flue is a duct, pipe, or opening in a chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors.
Lining Your Fireplace Insert Flue.  Where a wood-burning fireplace insert is vented into a chimney with an oversized flue, into an unlined chimney, or into a chimney with a damaged masonry liner, the chimney shall be refitted with a properly sized UL Listed metal or masonry liner.. -WABO Codebook (From NFPA 211).