Understanding Chimney Draft

Chimney draft, or the “stack effect,” is the movement of air into and out of buildings through an unsealed opening, chimney, or flue. It occurs due to the temperature difference between the indoor and outdoor air. Hot air is less dense than cold air, causing it to rise.

• Positive Draft: A good, positive draft pulls combustion gases up and out of the chimney, ensuring safe and efficient operation of your appliance.
• Poor Draft: Insufficient draft can be caused by a chimney that is too short, too cold, or improperly sized. This can lead to smoke spillage, poor combustion, and dangerous backdrafts.
• Excessive Draft: A draft that is too strong can pull too much heat out of the appliance, reducing its efficiency.

Disclaimer: This calculator provides a theoretical draft value. Real-world conditions like wind, chimney blockages, and house depressurization can significantly affect actual draft. This tool is for educational purposes only. Always consult with a certified chimney professional in your area for accurate diagnosis and service.