Fireplace repairs, from the damper to a new firebox

Masonry or factory-built: the first fork

Masonry fireplaces are assembled in place from brick, block and firebrick, each standing on a dedicated footing, under FBC Residential R1001. A factory-built fireplace is a listed metal firebox with refractory panels, installed as its listing directs under R1004 and tested to UL 127. The two fail differently and are repaired differently.

Masonry parts are repaired with masonry: firebrick, refractory mortar and parging. Factory-built parts are replaced with the maker's parts, following the installation manual, and a repair that alters the listed unit is off the table. Knowing which kind you have is the first step in working out the cost to repair a fireplace.

Nine fireplace repairs, smallest first

With access held equal, the order runs like this:

• Freeing a stuck damper and adjusting its handle or linkage.
• Re-hanging a damper plate, or replacing a broken handle.
• Repointing open firebox joints with refractory mortar.
• Replacing a few cracked or eroded firebricks.
• Replacing refractory panels in a factory-built unit, where parts are available.
• Parging a rough or cracked smoke chamber.
• Relaying a cracked or undersized hearth extension.
• Replacing a rusted-out throat damper, or fitting a top-sealing damper in its place.
• Rebuilding the firebox lining and its backing masonry.

Dampers: free, re-hang or replace

The throat damper is a cast-iron plate and frame just above the firebox opening. Under FBC Residential R1001.7.1, the damper is ferrous metal, sits no lower than 8 inches over the top of the opening, and works from inside the room. Rust, warping and a broken handle or linkage are the faults that stop it.

Freeing a stuck plate and adjusting the linkage is the lightest job. Re-hanging a plate that has dropped off its pivots comes next. Replacing a rusted-out damper can mean cutting the old frame out of the masonry, and where that is impractical, a top-sealing damper fitted at the flue's upper end takes over the job.

Firebrick and refractory joints

A masonry firebox is lined with firebrick laid in refractory mortar. FBC Residential R1001.5 calls for back and side walls of at least 8 inches of solid masonry when they are lined with firebrick 2 inches thick or more.

Heat cycles open the joints first, then crack individual bricks. Raking and repointing open joints with refractory mortar is the smaller job. Replacing cracked or eroded firebrick means cutting each one out and setting a new one, so firebox repair cost grows with the number of bricks and where they sit, since the back wall takes the most direct heat.

Parging the chamber above the damper

Between the damper and the flue, the smoke chamber narrows the fire's wide exhaust into the flue's small opening. R1001.8 calls for solid masonry walls with the inside parged smooth in refractory mortar, but a chamber built by stepping bricks inward and left unparged has a rough, ledged interior.

Parging coats that interior smooth with a refractory mortar, which improves the smoke path and closes gaps. It is worked through the damper opening from below in tight space, so its scope depends on the chamber's size and how much loose material has to come off first. A cracked or eroded chamber is itemized on the estimate.

Hearth and hearth extension

The hearth is the floor the fire sits on, and its extension is the noncombustible strip that reaches out into the room. R1001.10 sizes that strip at 16 inches deep and 8 inches past the opening on either side, and at 20 inches deep and 12 past each side for any opening of 6 square feet and up.

Loose tile on a sound extension is a small repair. A cracked extension, one short of those dimensions, or one resting on wood framing without noncombustible support is larger, because fixing it can mean breaking it out and relaying it to size.

Prefab repairs and the maker's parts list

Factory-built fireboxes are lined with refractory panels instead of firebrick. Cracked panels, a warped firebox, a damaged grille or failed chimney sections are replaced with parts listed for that unit. R1004.1 requires factory-built fireplaces to be installed to their listing, which rules out patching a panel with masonry or borrowing parts from another maker.

Parts availability matters most here. A current model's panels are a routine order. A discontinued model's parts can be hard to find, and when the firebox itself has failed with no listed parts left, the choice becomes replacing the unit, which is an installation job, not a repair.

When the firebox has to be rebuilt

A masonry firebox whose back wall is bowing, whose bricks are loose throughout, or whose masonry behind the lining has cracked needs a rebuild rather than spot repairs. The old lining comes out, the backing masonry is checked, and new firebrick is laid in refractory mortar to the code's dimensions.

No fireplace repair is larger, short of work on the chimney itself. It also reaches the damper and the hearth, so those lines are priced alongside it.

Working inside the house, at floor level

Fireplace repairs happen in the living space, at floor level, in a small opening. The room is protected from the hearth out to the doorway, the opening is sealed while old material comes out, and a narrow or shallow firebox slows every task. Smoke chamber work is done by reaching up through the damper, so a small damper opening limits which tools fit. That is one reason two smoke chambers of the same size can take different amounts of time.

Which fireplace findings can wait

Some findings are about looks and some are about heat. Stained firebrick, a chipped hearth tile or a stiff damper handle can wait for a convenient time.

An open firebox joint, a cracked firebrick with a gap behind it, a hearth extension that is too short or rests on wood, and a damper that will not open are about heat and smoke. Until those are fixed, the fireplace should not be lit. We mark each line so the difference is plain on the estimate.

When the fireplace is gas or electric

Those units are repaired to their manuals and covered by separate guides. In a masonry fireplace that holds a gas log set, the firebox, damper and hearth work above still applies, while the burner and controls are gas work priced as gas fireplace service.

Electric units have no firebox to reline and no flue to parge. Their repairs are parts and wiring inside the unit, and any new circuit is an electrician's work.