Factory-Built Fireplaces: Care and Limits

What makes a fireplace factory-built

A factory-built fireplace, often called a prefab or zero-clearance fireplace, is manufactured as a unit and installed in a wood-framed wall. Its chimney is a listed metal pipe that runs up through the house, usually inside a framed enclosure called a chase. At the top, the chase is closed with a metal chase cover, and the chimney pipe ends in a listed termination cap.

Not sure what you have? Our guide to masonry vs. factory-built chimneys shows how to tell.

Why the listing matters

These fireplaces are tested to a safety standard as complete systems. One manufacturer's manual we reviewed states that its fireplace is listed to UL 127, the standard for factory-built fireplaces, and that it must be used with that manufacturer's specific chimney series, termination caps, firestops, and supports.

The practical consequence is that you cannot mix parts freely. A different brand of chimney pipe, a generic cap, or an aftermarket accessory may not have been tested with your fireplace. CSIA has cautioned that retrofitting listed appliances with aftermarket parts outside the original specifications is common but has uncertain safety effects.

Typical restrictions in the manual

Manuals differ, but the one we reviewed is a good example of the kinds of limits to expect:

• Burn wood only, not coal, liquid fuels, or household trash.
• Use only the specified grate; replace a warped grate with the same part.
• Use only the approved glass doors.
• Do not alter the fireplace or accessories except as the manual allows.
• Do not install a wood or gas insert without written authorization from the manufacturer.

If you do not have your manual, the model and serial numbers are usually on a label inside the firebox or behind the lower grille. Manufacturers often publish manuals online.

What wears out

• Refractory panels. The inner firebox walls are refractory panels. Fine cracks are common. The manual we reviewed says panels should be replaced when cracks grow large enough that pieces dislodge or the metal behind is exposed. See inside the firebox.
• Warping. Overfiring, such as burning large amounts of paper or very hot fires, can warp metal parts.
• Dampers. Factory-built dampers can bind or break.
• Chimney pipe. Joints and inner walls can corrode, especially if water gets in from the top.
• Chase cover and cap. Exposed metal on the roof rusts over time.

Chase covers and water

The chase cover is the metal panel that closes the top of the framed enclosure. When it rusts, holds water, or loses its seal around the chimney pipe, water runs into the chase. That can rot framing, stain ceilings, and rust the fireplace below. Many original chase covers are flat galvanized steel, which is prone to rust. A replacement cover shaped to shed water, in a corrosion-resistant metal, is a common repair. See our chase covers service.

Cleaning and inspection

CSIA notes that factory-built fireplaces should be swept when appreciable buildup occurs, because creosote deposits are acidic and can corrode the metal components. Annual inspection under NFPA 211, as summarized by CSIA, applies to these systems too. Sweeping tools and methods should be suitable for metal chimney pipe.

The US Consumer Product Safety Commission recommends having flues and chimneys inspected before each heating season, opening the damper before lighting a fire and keeping it open until the ashes are cool, and never using gasoline or charcoal lighter fluid to start a fire.

Gas factory-built fireplaces

Many newer homes have factory-built gas fireplaces, usually direct-vent units with a sealed glass front and a coaxial vent pipe through the wall or roof. They are also listed systems with their own manuals. The same principle applies: use the manufacturer's vent components and replacement parts, and have the unit serviced by someone working from its manual. Gas logs should not be added to a factory-built wood fireplace unless the fireplace manufacturer allows that specific use. See our gas fireplace service.

Signs to have it checked

• Cracks in refractory panels with loose pieces, or bare metal showing.
• Rust in the firebox, on the damper, or on the grate.
• Water stains on the wall or ceiling near the chimney chase.
• Warped or discolored metal around the opening.
• Smoke escaping into the room. See why smoke comes into the room.

These are prompts for an inspection, not a diagnosis. If you see any of them, stop burning until the fireplace has been checked.

When repair is not the answer

Some factory-built fireplaces reach the end of their useful life. If the manufacturer no longer supplies parts, if the firebox metal is burned through, or if the chimney pipe is damaged in ways that cannot be fixed with listed parts, the safe options are usually to replace the unit with a new listed system or to stop using it. Patching with unlisted parts is not a safe substitute.

Next step

If your prefab fireplace has cracked panels, rust stains, or water in the firebox, stop using it until it is checked and request an inspection. See our fireplace repair and chase covers pages.

Questions homeowners ask

Sources

1. Majestic SSTB11 factory-built fireplace owner's manual
2. CSIA: Homeowner Resources and FAQ
3. US CPSC: CPSC Warns of Hazards from Heaters and Fireplaces
4. US EPA Burn Wise: Choosing Wood-Burning Appliances

This guide is general information. It can't diagnose a specific chimney; an inspection can.