Smoke rolling out under the mantel
A fireplace that spills smoke along the top of its opening is usually drawing too little air up the flue for the size of the opening. Some older fireplaces were built with openings large for their flues, and they have always done it.
A rough, stepped smoke chamber slows the draft further, and a house under negative pressure, with a kitchen hood or bathroom fans running, pulls air down the chimney. Fixes range from a smoke guard that reduces the opening height, to glass doors, to smoothing the smoke chamber with a parged coat.
Throat dampers and top-sealing dampers
The original throat damper sits just above the firebox. When the cast iron warps or rusts through, replacing it in place can be awkward, because it is built into the masonry.
A top-sealing damper mounts on the flue top and is worked by a cable down to the firebox. When closed it also keeps rain and animals out, which suits a fireplace that stays unused for long stretches. On a stack with several flues, each flue needs its own.
Tell us how long the fireplace has sat unused, whether the damper moves, and whether smoke has spilled when it was last lit. A short description, and a photo if you can take one safely, is a good start to an estimate request.
Firebrick, refractory mortar and the hearth
Cracked or loose firebrick is reset or replaced in refractory mortar made for firebox heat. Where the back wall has bowed forward, it is taken down and relaid.
The hearth extension, the non-combustible slab in front of the opening, matters as much. A crack right through it can let a dropped ember reach the framing underneath, which is why a cracked hearth is a repair item and not a cosmetic one.
Converting a formal fireplace to gas
Gas-fuelled fireplaces are not subject to South Coast AQMD no-burn alerts, and under Rule 445 a dedicated gas fireplace is one of the device types that may be permanently installed. A log set uses the existing firebox and flue; an insert usually needs a liner sized to it.
The City of San Marino decides any permit question for the gas line or the appliance. If you ever smell gas at a converted fireplace, leave the house and call the gas utility from outside.
What a repair estimate depends on
The number of fireplaces being brought back into use, the damper type and whether a top-sealing unit is fitted, how much firebrick and hearth work is needed, whether the smoke chamber needs parging, and any gas conversion parts. A stack with several flues multiplies the damper and cap work.