Monessen AI42AK43A Flue Block Plate. Monessen is a company that designs a large line up of upgraded fireplaces and stoves designed to make your existing fireplace or new wood burning stove really stand out with style and exceptional style and performance. This Monessen AI42AK43A Flue Block Plate mounts at the top of the fire place along with the ventilation sections. This Flue Block eliminates excess smoke from entering the chimney. When this Flue is installed correctly you can count on both safety of your home, and performance that you can rely on during all those colds days throughout the year.