The firebox is the area where the fire is contained and burned. A damaged or cracked firebox can occur due to excessive heating and cooling cycles, poor installation, or if anything other than wood is burned in a chimney. Common issues include cracked or crumbling brick, damaged mortar joints, and deteriorated refractory panels. While minor cracks and damage may not appear too concerning, this issue can worsen if left untreated and may lead to fireplace functionality issues and carbon monoxide poisoning within your home or business. Thus, it should be treated by professionals as soon as possible.