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Fireplace & Chimney Clearance Guide

Planning a mantel, new flooring, a basement finish or a roof change? Check these first. They’re the minimum clearances for traditional masonry (brick or stone) fireplaces and chimneys.

Mantel & trim Hearth extension Air space to framing Chimney height Switching to gas

Factory-built fireplace, insert or stove? Those have their own listed clearances in the manufacturer’s manual — those numbers win over anything here.

1 · Mantel & trim

No wood trim, mantel or other combustible material within 6″ of the fireplace opening — top or sides.
Anything above the opening that sticks out more than 1-1/2″ must be at least 12″ above it. That’s where a mantel shelf belongs.

Pulling a permit? The Minnesota Residential Code is stricter between 6″ and 12″: trim can project only 1/8″ per inch of distance (3/4″ at 6″, 1-1/4″ at 10″). Build to the stricter number and you’ll pass either way.

NFPA 211 §11.2.5.3–11.2.5.4

2 · Hearth extension

Opening under 6 sq ft: noncombustible hearth at least 16″ in front and 8″ past each side.
Opening 6 sq ft or more: at least 20″ in front and 12″ past each side.
At least 2″ thick. Front distance is measured from the facing material.

Replacing floors? Keep wood and carpet out of this area.

NFPA 211 §11.3.2–11.3.4

3 · Air space to framing

2″ between a masonry fireplace’s front and sides and wood framing; 4″ at the back.
2″ around an interior chimney; 1″ for an exterior chimney.
Keep the gap empty — no insulation, spray foam or drywall packed against the masonry. Firestop only at headers and floor lines with sheet metal or thin noncombustible board.

Opening a wall during a remodel is the best time to check this — call before you close it up.

NFPA 211 §11.2.5.1–11.2.5.2, §7.3.1, Table 7.2

4 · Chimney height

At least 3 ft above the highest point where it passes through the roof, and
At least 2 ft higher than anything within 10 ft horizontally.
Adding a dormer or second story nearby can make an existing chimney too short.

Meeting code doesn’t guarantee good draft. When part of the house is taller than the chimney, warm air leaking out of the upper floors pulls outside air in down low — and the chimney can become that air intake, pulling cold air and smoke into the house. That’s the stack effect, and the fix is sometimes more chimney height, not a new liner.

NFPA 211 Table 7.2, §4.2

Not sure? Text a photo of your fireplace and a quick sketch of your project to 612-402-9249 and we’ll tell you if anything looks close.

Switching to gas?

Gas doesn’t make a fireplace code compliant

A common assumption: “It’s gas now, so the old fireplace problems don’t matter.” They still do. Gas logs and gas inserts are built to go into a fireplace that already meets code. They don’t fix, replace or grandfather the fireplace around them.

Gas logs are listed for a solid-fuel fireplace with a working chimney flue, built of noncombustible materials. Wood framing against the firebox, a cracked firebox or a failing flue is still a defect.
Gas inserts install into an existing fireplace that has to be sound and built to code. Most manuals also call for a liner to the top and have their own clearances to mantels and trim — sometimes more than the fireplace alone.
Gas still makes carbon monoxide and water vapor. The flue has to be intact and sized for the appliance, and the damper set the way the manual says.

NFPA 54 (National Fuel Gas Code) §10.6.3; International Fuel Gas Code §602.1. Always follow the gas appliance’s installation manual.

Before a gas conversion, we check

Firebox and smoke chamber condition
Flue liner condition and size for the gas appliance
Clearances: mantel, trim, hearth extension and framing
Damper: removed, clamped or left operable per the manual
Chimney height and draft

Then you know the fireplace is ready for gas before anyone runs a gas line.

Call 612-402-9249