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Chimneys and Fireplace Sizing

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Chimneys can be separated in two main categories:

  • metal
  • masonry

Prefab or Metal Chimneys

Prefab or metal chimneys, class A and double or triple walls are usually found in three diameters. Each diameter has a specific usable 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.

Chimneys - Prefab or Metal
Chimney SizeCommon Venting Uses
Inside diameter

Inside Area
(square inches)

6 28.3 Stoves, Central Heaters
7 38.5 Stoves, Central Heaters
8 50.3 Stoves, Small Fireplaces, Central Heaters
10 78.6 Stoves, Fireplaces, Central Heaters
12 113 Fireplaces, Central Heaters

Masonry Flues

Masonry Flues
Flue SizeCommon Venting Uses
Outside Diameter
Inside Area
(square inches)

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
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Related Topics


Combustion processes and their efficiency. Boiler house and chimney topics. Properties of fuels like oil, gas, coal and wood and more. Safety valves and tanks.

Heating Systems

Design of heating systems - capacities and design of boilers, pipelines, heat exchangers, expansion systems and more.

Related Documents

Chimney Sizing

Calculate chimney draft and required chimney area - online calculator.

Chimney's Explosion Doors

Recommended size of explosion doors or draught stabilizers in oil fired installations.

Chimney's Size vs. Boiler Power

The size of chimney vs. boiler's heat load.

Chimneys - Roof Termination

Chimneys and single wall vents roof termination.

Fuel Oil Burners

Pot types, gun types and rotary types fuel burners.

Natural Draft - Air Flow Volume and Velocity

Air flow - volume and velocity - due to stack or flue effect caused by indoor hot and outdoor cold temperature difference.

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