It’s true .. many Furnace and Hot Water Heaters vent up your brick chimney. The Brick structure itself is called the chimney and within this chimney structure, you can have multiple systems venting up this one chimney. There is a wythe wall creating separate channels for each system to vent which also includes terra cotta clay flue tiles which are stacked on top of each other to create the lining of each system. Although you may not ever use your fireplace it is important to have your chimney checked to make sure your furnace system is clear and safe from any obstruction. Any obstruction or blockage such as a birds nest could cause carbon monoxide to come back into your home and create a dangerous situation. Have your chimney checked annually to make sure it’s safe.