The Physics of Chimney Draft: How Your Stove Breathes
Understanding the pressure differences that make or break a clean burn.
A wood stove is not an island; it is part of a complex pressure system. The chimney's job is to create a vacuum (draft) that pulls fresh air into the stove and pushes smoke out. If your draft is too weak, smoke spills into the room. If it's too strong, your wood burns too fast and wastes heat.
Stack Effect and Temperature
Draft is created by the Stack Effect: hot air is less dense than cold air and wants to rise. The greater the temperature difference between the flue gases and the outside air, the stronger the draft. This is why stoves often struggle to start on a warm fall day but roar during a sub-zero winter night.
The Height Factor
Chimney height is the second major factor in draft. A taller chimney provides more 'stack' for the pressure difference to build. However, going too tall can cause the gases to cool down too much before they exit, leading to creosote buildup. Our draft calculator helps you find the sweet spot for your specific stove and altitude.
FAQ
What is 'Backdraft' and how do I fix it?
Backdraft occurs when air pressure outside is higher than inside, or when powerful kitchen fans pull air down the chimney. Cracking a window near the stove during startup is the most common fix.