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Engineering ToolBox > Chimneys and Fireplace Sizing
Chimneys can be separated in two main categories:
Prefab or metal chimneys, class A and double or triple walls are usually found in three diameters. Each diameter has a specific useable area, which is also called it's cross section.
The capacity of a chimney to remove smoke and/or energy (BTU's) from an appliance is directly related to the cross section area.
| Chimney Size | Square Inches | Common Venting Uses |
| 6 Inch Inside Diameter | 28.3 | Stoves, Central Heaters |
| 7 Inch Inside Diameter | 38.5 | Stoves, Central Heaters |
| 8 Inch Inside Diameter | 50.3 | Stoves, Small Fireplaces, Central Heaters |
| 10 Inch Inside Diameter | 78.6 | Stoves, Fireplaces, Central Heaters |
| 12 Inch Inside Diameter | 113 | Fireplaces, Central Heaters |
| Flue Size (Outside Diameter) | Square Inches | Common Venting Uses |
| 7 1/2 X 7 1/2 | 31 | Stoves, Central Heaters |
| 8 1/2 x 8 1/2 | 41 | Stoves, Central Heaters |
| 8 1/2 X 13 | 70 | Stoves, Fireplaces, Central Heaters |
| 13 X 13 | 99 | Fireplaces |
| 13 X 18 | 156 | Fireplaces |