Gas fireplace insert liner kit installation for Simpsonville's masonry fireplaces — a gas insert does not use the existing clay tile flue. It needs a dedicated small-diameter stainless liner through the existing chimney, sized to the insert manufacturer's specifications. Liner confirmed before installation begins.
The most common misunderstanding when installing a gas fireplace insert into a Simpsonville masonry fireplace: homeowners assume the insert will simply use the existing clay tile flue, the same as a wood fire does. It does not. A gas insert is a sealed appliance with its own combustion chamber — it requires a dedicated liner matched to its venting specifications.
Open masonry firebox — combustion occurs in the open masonry chamber, smoke rises directly into the smoke chamber above.
Smoke and combustion gas rise through the full interior diameter of the existing clay tile liner — typically 8×8, 8×12, or 13×13 inches, depending on firebox size.
The full existing clay tile liner is the active flue path — liner condition directly determines safety and performance of each fire.
Combustion air drawn from the room through the open firebox opening — no sealed combustion air inlet.
Sealed metal firebox slid into the existing masonry opening — combustion occurs inside the insert's sealed chamber, not in the masonry firebox.
A small-diameter stainless liner (typically 3-inch or 4-inch for direct-vent, or larger for B-vent inserts) runs from the insert's flue collar up through the existing masonry chimney to terminate at the top. The clay tile liner is bypassed.
The existing clay tile liner is not active — its condition does not affect the insert's operation. The insert's own dedicated liner is the active flue path.
Direct-vent inserts draw combustion air through the outer sleeve of a coaxial liner — a sealed system that does not require room air for combustion.
The liner itself — a flexible stainless tube in the diameter specified by the insert manufacturer. Routed from the insert's flue collar through the existing masonry chimney to the chimney top. Navigates any offsets in the existing chimney structure.
Connects the new flexible liner to the insert's flue outlet at the bottom. Seals the connection point at the insert face — prevents flue gas from entering the gap between the insert and the masonry surround.
A stainless plate installed at the chimney crown that seals the existing clay tile liner opening and secures the new insert liner. The top plate closes the space between the new insert liner and the old tile liner — preventing rain, debris, and outside air from entering the chimney through the old liner.
A cap specific to the insert liner diameter — covers the liner opening at the chimney top and prevents rain and debris from entering the new liner. Cap style depends on whether the insert uses a single flue (B-vent) or coaxial direct-vent liner with separate air intake and exhaust ports.
Most modern gas fireplace inserts installed in Simpsonville are direct-vent appliances. A direct-vent insert draws combustion air from outside through one passage while exhausting flue gas through a separate passage — both routed through the same chimney. The liner kit for a direct-vent insert is a coaxial liner: a smaller exhaust tube runs inside a larger outer tube that routes combustion air downward. Both are installed as a single flexible assembly through the existing masonry chimney. The specific coaxial liner diameter is determined by the insert unit's manufacturer specifications and cannot be substituted.
| Liner Type | Typical Diameter / Size | Determined By | Notes |
|---|---|---|---|
| Existing clay tile — standard residential fireplace | 8×8, 8×12, or 13×13 inch square/rectangular tile | Original firebox size and NFPA 211 ratio | Remains in place but inactive after insert installation |
| Gas insert liner — B-vent (natural draft) | 4-inch, 5-inch, or 6-inch round flexible liner | Insert BTU input and flue height | Single liner — exhaust only, room air for combustion |
| Gas insert liner — direct-vent (coaxial) | 3/5-inch or 4/7-inch coaxial (inner/outer diameter) | Insert unit's manufacturer specification | Diameter is unit-specific — cannot deviate from manufacturer spec |
| Gas insert liner — high-BTU direct-vent | 5/8-inch coaxial or single 6-inch exhaust | Insert BTU rating and manufacturer specification | Larger BTU units require larger liner diameter — confirmed before ordering |
The insert unit's make, model, and BTU input are confirmed before liner is ordered. The manufacturer's installation manual specifies the required liner diameter and type — direct-vent coaxial or B-vent single liner. Liner ordered to the exact specification; no substitution.
The existing chimney height and any offsets in the flue path are measured before liner length is cut. A flexible liner navigates offsets in the existing masonry chimney without requiring access at each bend point. Total liner length confirmed before installation begins.
The new insert liner is routed downward from the chimney top through the existing clay tile flue. For a coaxial direct-vent liner, both the inner exhaust tube and outer combustion air tube are inserted together as one assembly. Bottom end positioned to connect to the insert's flue collar.
The top plate is fitted over the liner at the chimney crown — sealing the existing clay tile liner opening and securing the new insert liner in position. The termination cap is installed on the liner at the chimney top, appropriate to the liner type (single exhaust or coaxial air/exhaust ports).
The adapter collar connects the liner to the insert's flue outlet. The insert is slid into the masonry opening, the face plate covers the masonry surround, and the connection at the flue collar is secured and sealed. Final inspection confirms liner is clear, sealed, and properly terminated before the gas connection is made.