To block a flue effectively, use a chimney balloon, sealant, or airtight damper. Ensure the flue is completely closed when not in use to prevent drafts, smoke, or exhaust gases from entering living spaces. For permanent blocking, consult a professional to assess structural integrity and local building codes. Short-term solutions like foam insulation or heavy-duty tape can temporarily seal gaps but require re-evaluation after high-heat events. Always prioritize safety by verifying that blocked flues do not compromise ventilation or create fire hazards.

Blocking flues is critical to mitigating risks of carbon monoxide (CO) poisoning and improving energy efficiency. CO, a colorless, odorless gas, accounts for approximately 400 annual deaths in the U.S., often linked to faulty heating systems or blocked vents (CDC, 2022). Sealing flues reduces the risk of exhaust gases entering homes, particularly during winter heating. A study by the Department of Energy found that properly sealed chimneys can cut heat loss by 10–20%, saving homeowners $100–$300 annually (DOE, 2021). However, improper blocking may lead to CO buildup or fire risks, emphasizing the need for professional inspection. Building codes in many states, such as California and New York, mandate flue covers or restrictions during certain seasons to prevent emissions from entering occupied spaces (International Code Council, 2021). Balancing safety and efficiency requires balancing temporary fixes with long-term compliance, ensuring flue integrity aligns with both health and environmental regulations.