Building a Masonry Fireplace

Fireboxes

• Masonry fireplace boxes contain the fire. They must have enough thickness to accommodate the fire so the high levels of heat contained within do not ignite anything. Refractory mortar works best for fireplace masonry, since Portland cement cannot handle the heat of the fireplace as well, and may sustain damage once the fireplace cools below 600 degrees Fahrenheit after rising above that temperature. This causes the Portland cement--based mortar to expand and damage the masonry work. Refractory mortar does not expand when heated and cooled.

Chimney

• The metal damper in a masonry fireplace should have at least 12 inches of clearance above the fireplace opening, and the chimney should have at least 2 inches of air space. Well-constructed fireplace chimneys do not inhibit burning exhaust and allow the exhaust to leave the home safely and efficiently. The chimney must be at least 3 feet above the highest point of the roof and at least 2 feet above any structures within 10 feet of the chimney.

Mantel

• The mantel is the design built around the fireplace. Choose between a mantel that hangs on the wall or a freestanding mantel. Built-in mantels need wood mortared into the fireplace for support. Make sure the fireplace does not have combustible materials that the fireplace heat can radiate toward and ignite. Have at least 8 inches of masonry wall and 12 inches of distance between the fireplace and anything combustible.

Flue

• The flue is the space through which the fireplace exhaust travels. Clay flue liners need to be enclosed in at least 4 inches of masonry. The flue must not change shape more 6 six inches from the point where the chimney passes through the ceiling. Flues can discharge the byproducts of the fireplace with other flues as long as the flues don't slope more than 30 degrees from traveling perfectly upward, and as long as the flues are discharging the same byproducts, since different byproducts can combine and cause chemical reactions.

Other Features

• Seal the fireplace with a metal or glass door, which keeps heat and cinders from leaving the fireplace, but allows you to set up logs. Place a metal cap on the chimney top to prevent animals from entering, but leave enough clearance for the exhaust to escape.