Proper Fireplace Flue Size

Chimney Size Importance

• A chimney or flue system must be of a proportionate size to its corresponding fireplace to adequately remove smoke and particulate matter from the immediate area. A flue or chimney that's too small for the fireplace can clog easily with soot or creosote. This is especially true for a fireplace that burns solid matter, including wood, for fuel. A clogged chimney or flue can cause smoke carrying dangerous chemicals to back up into a home. Inhaling smoke from fuel burning can lead to carbon monoxide poisoning. Prolonged exposure to this odorless chemical can cause breathing difficulties, unconsciousness and death.

Small Metal Fireplaces

• A small prefabricated metal fireplace can be a standalone unit or an appliance built into the wall of a new home. The device can provide heat for one room of a house, but may struggle to heat an entire floor. According to Hearth.com, a home heating information website, a small fireplace measuring up to 50.3 square inches requires a flue or chimney with at least an 8-inch inside diameter. This provides sufficient space for smoke and fumes to funnel up the stack and away from the property.

Larger Metal Fireplaces

• A larger prefabricated metal fireplace can heat an entire floor of a home depending on its size and how much fuel the design can burn at any one time. According to Hearth.com, a metal fireplace measuring up to 78.6 square inches requires a chimney or flue with an inside diameter of at least 10 inches. A metal fireplace measuring up to 113 square inches needs a venting system with an inside diameter of at least 12 inches. The flue collar -- the device attaching the flue to the fireplace -- on a chimney should always match the inside diameter of the chimney or flue system to prevent any smoke from escaping.

Masonry Fireplace Flues

• A masonry fireplace does not use prefabricated components like a metal fireplace. This type of fireplace uses brick or stone as the main building component and can be almost any size depending on the builder's design and the homeowner's space restrictions. According to Hearth.com, the popular size range for masonry fireplace varies between 32 to 36 inches wide and 25 to 29 inches high. The flue size for a masonry fireplace varies based on the size of the fireplace opening. It's common for the fireplace opening to be 10 times the size of the flue or chimney diameter in inches.