Local fireplace installation in Jacksonville Beach

A hearth extension you can see

For a factory-built fireplace, the code sends the hearth extension to the listing and adds one visible rule: it has to be readily distinguishable from the floor around it. The reason is simple. People need to see where the fire-safe zone ends so they keep rugs and furniture off it. Listed hearth extensions are tested to UL 1618, and the manual gives the size, the materials and any thermal requirement under the surface.

We build the extension to those figures and finish its edge so the line is plain. On a raised design, the manual also says whether the extension can sit on the floor or has to be built up.

Firebox depth and wall thickness

The firebox of a masonry fireplace is at least 20 inches deep under the code. Its back and side walls are 8 inches of solid masonry including a 2-inch firebrick lining, or 10 inches where there is no lining. Firebrick meets ASTM C27 or C1261, and the joints between the bricks, laid in medium-duty refractory mortar, stay no wider than a quarter inch. Those numbers are what keep the heat of the fire inside the masonry and away from the framing that sits a couple of inches beyond it. We lay the firebox before the smoke chamber, and the inspector can see the lining thickness at the opening.

A spark arrestor sized to the flue

Where a masonry chimney has a spark arrestor, the code sets its size and mesh. Its net free area is at least four times the area of the flue outlet it covers. The screen is heat and corrosion resistant, equal to 19-gage galvanized or 24-gage stainless steel, with openings that stop a 3/8-inch sphere but pass a 1/2-inch one. It also has to be reachable for cleaning.

On a factory-built chimney, the listed cap does this job, and it is the cap from the chimney maker's list. Mesh that clogs with soot restricts the draft, so the screen gets checked at each yearly inspection.