If a flue is broken, prioritize immediate safety by stopping all use of the affected appliance or fireplace. Evacuate the premises and avoid returning until the issue is resolved. Contact a licensed HVAC or masonry professional to inspect and repair the flue, as DIY repairs risk further hazards.

A broken flue fails to vent toxic combustion gases, including carbon monoxide (CO), which can lead to poisoning or death. The CDC reports that CO poisoning causes over 500 deaths annually in the U.S., with faulty ventilation systems contributing to 40% of cases. A compromised flue allows CO to accumulate rapidly, as evidenced by a 2021 study in Environmental Science & Technology showing CO levels exceeding 400 ppm (the immediate danger threshold) within 15 minutes in homes with damaged flues. Additionally, the Consumer Product Safety Commission (CPSC) estimates that 1 in 6 residential CO poisonings stem from blocked or damaged chimneys, underscoring the urgency of professional repair. Delaying fixes increases health risks, as even minor cracks can permit dangerous gas leaks. Proactive maintenance, such as annual flue inspections, reduces incidents by 60%, per data from the National Fire Protection Association (NFPA). Always prioritize certified technicians, as improper repairs may exacerbate structural damage or fire risks.