Flue Section Calculation

Foundation and Size

• The overall size of the chimney can affect the size of the chimney flue. The foundation of the chimney should be constructed from masonry or concrete that is a minimum of 12 inches thick to withstand the heat generated in a fireplace. The overall width of a fireplace structure is typically between 30 and 36 inches for every 300 square feet encompassed by the family room, living room or any other room in which the fireplace is located. These specifications are adjustable for larger rooms as necessary.

Flue Size

• Calculation of the flue size for most fireplaces depends largely upon the size of the fireplace opening. A rectangular flue should be at least one-tenth the size of the fireplace opening. If more than one opening exists, the same rule still applies but based on the combined area of both flues. For liners that consist of a round flue, the opening should be a least one-twelfth of the size of the opening.

Location

• The location of the flue liner is important in keeping the fireplace safe and resistant to heat buildup. The opening of the flue should begin at a point no less than 8 inches below the top of the fireplace's smoke chamber. It is also essential that the chimney be at a 90 degree angle to the ground with as little sloping as possible. Your Way Fireplaces recommends that the chimney be no more than 30 degrees off vertical.

Other Considerations

• Various other factors can play a role in determining the size of a chimney flue. For instance, the type of the vent pipe, its lateral length, the height of the chimney and any type of connectors that may used in venting the chimney can all factor into the final calculation of the flue size. Having a professional consultant or engineer help you with the proper design of your chimney is essential for safety considerations.