Flue Liner Types & Installation Flashcards

When relining a chimney used by a high-efficiency gas furnace (Category IV appliance), which liner material is required?

Answer: AL29-4C or equivalent high-alloy stainless steel

Category IV appliances produce positive-pressure, moisture-laden, acidic flue gases requiring AL29-4C or equivalent corrosion-resistant alloy liners.

What is the purpose of a top plate (liner top plate or rain cap plate) in a flexible liner installation?

Answer: It secures the liner at the chimney crown and supports the rain cap

The top plate anchors the liner at the chimney crown, seals the annular space, and provides a mounting point for the rain cap.

A masonry chimney serves both a fireplace and a gas water heater through separate flues. A sweep finds a hole connecting the two flues inside the chimney. What is the primary hazard?

Answer: Carbon monoxide from the water heater can enter the fireplace flue and the living space

Interconnected flues allow CO-laden exhaust from the gas appliance to migrate into other flue passages and potentially into the home.

Which installation detail is critical when terminating a flexible liner at the appliance connector tee at the base of the chimney?

Answer: The liner must be sealed to the tee with listed components to prevent flue gas leakage

The connection between the flexible liner and the appliance tee must be sealed with listed components to prevent combustion gas from leaking into the chase or living space.

In a masonry chimney, the annular space between a new flexible liner and the original flue tile should be:

Answer: Filled with listed insulation or left open per manufacturer instructions

The annular space may be filled with listed insulation for performance improvement or left open as the manufacturer specifies; non-listed insulation materials are not approved.

What minimum overlap is typically required at joints between rigid stainless steel liner sections?

Answer: 3 inches

A minimum 3-inch overlap at rigid liner section joints ensures adequate connection strength and reduces the risk of separation during thermal expansion.

When a cast-in-place liner system is installed, how is the form removed from the cured liner?

Answer: The inflatable form is deflated and pulled out after the material cures

Cast-in-place systems use an inflatable bladder or form that is deflated and withdrawn after the liner compound cures around it, leaving a smooth cylindrical liner.