When an aging clay-tile flue fails to meet the diameter requirements of a new high-efficiency gas boiler or furnace, the entire heating system becomes a liability. The Z-Flex 5" x 35' Aluminum Liner Kit (MPN: 2GACKIT0535) resolves that situation in a single afternoon. This UL 1777-listed, 2-ply corrugated aluminum chimney liner ships as a complete venting kit — liner, rain cap, mortar collar, flashing, and screws included — purpose-built for Category I natural-draft gas-fired appliances operating below 470°F.
Rated for natural gas and propane fuel sources, the 2GACKIT0535 covers 35 linear feet of flue travel, fitting any masonry or factory-built chimney with a minimum 5-5/8" × 5-5/8" interior dimension. Professional HVAC technicians and plumbing contractors choose this specific model when the job calls for a single-run liner in a mid-height residential chimney — no additional sections, no field splicing, no guesswork about whether 25 feet will clear the roofline.
How Z-Flex's Triple-Lock Seam Keeps Combustion Gases Out of Living Spaces
The structural core of the 2GACKIT0535 begins with a dead-soft aluminum strip that is spirally wound under controlled tension, then mechanically joined along its full 35-foot length using a triple-lock seam.
That seam matters more than any other single manufacturing detail. Flue gas — a mixture of water vapor, carbon dioxide, nitrogen oxides, and trace combustion byproducts — travels under natural draft pressure through the liner's 5-inch interior bore. Any seam failure creates a pathway for those exhaust gases to migrate into chase cavities or living areas. Z-Flex's triple-lock joint closes that risk mechanically, without relying on epoxy, resin adhesives, or field-applied sealant that can crack under thermal cycling.
The aluminum itself is selected for its dead-soft temper, meaning the metal deforms predictably under bending rather than fracturing. When an installer feeds 35 feet of liner down a chimney with offsets or slight misalignment, the 2GACKIT0535 flexes through those angles without stress concentrations forming at the seam.
What the 2-Ply Aluminum Wall Construction Means for Long-Term Flue Gas Resistance
Two discrete layers of corrugated aluminum, each formed independently and then combined, give the 2GACKIT0535 a wall structure that outlasts single-ply alternatives in gas venting service.
The inner ply contacts flue gas on every combustion cycle. Natural-draft Category I appliances — including gas fireplaces, residential boilers, atmospheric water heaters, upflow furnaces, and unit heaters — exhaust at temperatures that remain below the 470°F rated ceiling of this liner. Within that operating band, aluminum resists the mildly acidic condensate that forms during appliance startup and cool-down, when flue gas temperatures briefly dip before the chimney draft fully establishes.
The outer ply adds puncture resistance during installation. Feeding a flexible aluminum chimney liner past old mortar ledges, clay tile joints, and debris inside a masonry flue exposes the liner to abrasion. A single-layer wall is vulnerable at those contact points; the 2-ply construction of the 2GACKIT0535 absorbs that contact without compromising the inner sealing surface.
Deep corrugations pressed into both plies provide the flexibility HVAC contractors depend on for navigating chimney offsets up to the angles permitted under UL 1777 and NFPA 211 installation guidelines. Those corrugations are not incidental — they are precisely spaced to distribute bending stress evenly rather than concentrating it at any single point along the 35-foot run.
Which Gas Appliances & Fuel Types Work with the 2GACKIT0535's 5-Inch Bore
The 5-inch internal diameter of this aluminum chimney liner matches the outlet collar dimensions of a wide range of Category I atmospheric-vented gas appliances commonly installed in residential and light commercial settings.
Compatible fuel gas types include natural gas distributed through municipal supply lines and propane delivered from on-site tanks. The liner's aluminum construction handles the exhaust chemistry of both fuel gases without the corrosion risk that would appear with improper liner materials in oil or solid fuel combustion applications.
Appliances served by this liner diameter typically include:
- Gas fireplaces and fireplace inserts requiring a 5" outlet connection (Z-Flex recommends adapter 2ZSCPRP05 for secure fireplace insert connections)
- Atmospheric gas boilers with 5" flue collars found in residential heating systems up to moderate BTU ratings
- Natural-draft gas water heaters venting to masonry chimneys in multi-story residential construction
- Upflow and counterflow gas furnaces operating in Category I configuration
- Unit heaters in garages, workshops, and light commercial spaces
The 2GACKIT0535 is not rated for Category II, III, or IV appliances — including condensing furnaces and boilers that produce positive flue pressures or generate acidic condensate in the exhaust system. Those appliances require stainless steel liner systems with positive-pressure ratings.
Why Does the 2GACKIT0535's 35-Foot Length Eliminate On-Site Splicing in Most Residential Chimneys?
Thirty-five feet covers the full flue travel distance in the overwhelming majority of single-family and low-rise multi-family residential chimneys, allowing HVAC technicians to complete the liner installation as a single continuous run without field connections.
Every field connection point on a flexible aluminum chimney liner represents a potential leak path. NFPA 54 (the National Fuel Gas Code) and NFPA 211 (Chimneys, Fireplaces, Vents) restrict the number of allowable joints inside a chimney liner for exactly this reason. By arriving at the job with 35 feet of liner in a single piece, the 2GACKIT0535 avoids those concerns entirely on chimneys from one to three stories.
The liner ships compressed — factory-wound to a fraction of its installed length — which simplifies shipping logistics and job-site handling. A single installer can carry and position the liner before extending it down the flue from the chimney crown. The 16" × 16" galvanized steel flat flashing included in the kit anchors the liner at the crown, while the galvanized steel mortar collar seals the liner-to-chimney interface against wind, rain, and debris infiltration.
The aluminum rain cap included in the 2GACKIT0535 closes the top of the 5-inch bore against bird nesting, windblown debris, and precipitation. Bird-proof construction on the cap prevents the chimney obstructions that trigger carbon monoxide accumulation events when exhaust gas backflow occurs in a blocked flue.
UL 1777 & ULc S635 Listing: What Certification Means for Code Compliance & Permit Approval
The 2GACKIT0535 carries a UL 1777 listing and ULc S635 Class 1 certification — the dual-standard evaluation that satisfies building officials and AHJs (Authorities Having Jurisdiction) across the United States and Canada for gas venting liner installations.
UL 1777 specifically governs chimney liners for gas-fired appliances. The standard evaluates the liner's ability to contain flue gas, resist structural degradation across thermal cycling, and maintain mechanical integrity during installation. Passing UL 1777 means the 2GACKIT0535 has been independently tested — not self-certified by Z-Flex — to perform as a gas venting component under real operating conditions.
ULc S635 extends that certification into Canadian markets, reflecting testing against Canadian gas venting standards. Contractors working across both jurisdictions can specify the 2GACKIT0535 without maintaining separate liner inventories for U.S. and Canadian projects.
The listing also directly supports permit approval. When a homeowner or contractor pulls a mechanical permit for a gas appliance replacement that requires chimney relining, the inspection authority will ask for the liner's listing documentation. A UL 1777 / ULc S635 product clears that checkpoint without variance requests or additional documentation from the manufacturer.
Complete Kit Contents: Every Component Needed from Chimney Crown to Appliance Collar
The 2GACKIT0535 arrives as a fully configured installation kit, so contractors don't need to source components from multiple vendors or make additional trips for missing hardware.
The complete contents of this aluminum chimney liner kit include:
- 35-foot 2-ply corrugated aluminum liner — 5" internal diameter, shipped compressed
- Aluminum rain cap — bird-proof, sized for 5" liner termination at chimney crown
- Galvanized steel mortar collar — seals the liner-to-masonry interface at the chimney top
- Galvanized steel flat flashing — 16" × 16" base plate that secures to the chimney crown
- Self-tapping screws (3) — for securing liner connections at the top assembly
The aluminum rain cap is matched specifically to the 5-inch bore of this liner, eliminating the sizing errors that occur when installers source caps independently. The galvanized steel flashing and mortar collar are pre-sized for standard chimney crown dimensions, reducing field fabrication time on straightforward installations.
How Does the 2GACKIT0535's 470°F Temperature Rating Protect Against Liner Failure in Gas Service?
Category I natural-draft gas appliances produce exhaust gas temperatures that typically range from 300°F to 450°F at the appliance flue collar — well within the 470°F continuous service limit of this aluminum chimney liner.
That 470°F ceiling is the product of Z-Flex's aluminum alloy selection, corrugation geometry, and 2-ply wall construction working together. It is not a theoretical number — it is the temperature at which sustained liner integrity is guaranteed under the UL 1777 test protocol.
Gas combustion in atmospheric-vented appliances proceeds at controlled air-to-fuel ratios that limit flue gas temperatures relative to oil combustion or wood burning. This is why the 2GACKIT0535 is suitable for gas service but explicitly excluded from oil-fired boiler and furnace applications, where exhaust temperatures and the sulfur content of the fuel can exceed aluminum's long-term resistance threshold. For oil appliances, stainless steel chimney liner systems — typically 316L alloy for oil — provide the corrosion resistance that aluminum cannot deliver against sulfurous combustion acids.
For the gas appliances this liner is rated to serve, the 470°F ceiling provides a meaningful safety margin above normal operating temperatures, accounting for startup transients, appliance malfunctions, and reduced-draft conditions.
Installation Clearance Requirements: Fitting the 5" Liner into an Existing Masonry Flue
The 2GACKIT0535 requires a minimum chimney interior dimension of 5-5/8" × 5-5/8" to install correctly — a specification that guides the pre-installation inspection every HVAC technician should complete before ordering this liner.
That 5/8" clearance around the 5-inch liner exterior serves two purposes. It allows the installer to feed the compressed liner down the flue without binding against the tile walls, and it provides a small annular space for the mortar collar to seal properly at the chimney crown. Attempting to force a 5" liner into a flue with less than 5-5/8" of interior clear dimension risks kinking the liner during installation, which can compromise the triple-lock seam.
Older masonry chimneys with round clay tiles may require measurement at the narrowest point — often where tiles have shifted or cracked. Square flue tiles sized at 4.5" × 8.5" nominal interior are too small for the 2GACKIT0535; the next tile size up (typically 7.5" × 7.5" nominal interior) accommodates this liner with adequate clearance.
Installations into factory-built metal chimneys require verification of the specific manufacturer's liner compatibility before ordering.
Frequently Asked Questions About the Z-Flex 2GACKIT0535
Q: Can the 2GACKIT0535's 35-foot aluminum liner be cut shorter if my chimney measures less than 35 feet?
A: Yes — the 2-ply corrugated aluminum construction of the 2GACKIT0535 can be trimmed to the exact length needed using tin snips or aviation shears at the job site. Contractors working on two-story chimneys that measure 22 or 28 feet, for example, cut the liner to match the measured flue height before inserting. The triple-lock seam remains intact through the cut end; no field sealing of the cut edge is required. The included components — flashing, mortar collar, and rain cap — all size to the 5" liner bore regardless of the trimmed liner length.
Q: Does the 2GACKIT0535 work with a gas fireplace insert, and are any additional adapters needed for that connection?
A: The 2GACKIT0535 is rated for gas fireplace venting, but Z-Flex specifically recommends using adapter 2ZSCPRP05 to create a secure, leak-free connection between the liner's 5-inch corrugated aluminum end and a fireplace insert's oval or round exhaust collar. Without the adapter, the corrugated liner end may not seal tightly against the insert's exhaust fitting, which can allow flue gas to bypass the liner connection. For straight appliance collar connections on gas boilers, water heaters, and furnaces, the liner connects directly using the included screws.
Q: What is the warranty coverage on the Z-Flex 2GACKIT0535 aluminum chimney liner?
A: Z-Flex backs the aluminum liner component of the 2GACKIT0535 with a 25-year liner warranty, reflecting the company's confidence in the triple-lock seam construction and 2-ply aluminum wall integrity under normal Category I gas venting service. The warranty applies to the liner itself and covers defects in materials and seam construction. The included kit components — flashing, rain cap, mortar collar, and screws — carry separate coverage terms. Customers should retain installation documentation, including the appliance model and the liner installation date, to support any future warranty service claim.
Plumbing Supply & More: Professional-Grade Venting Components for Every Gas Installation
Plumbing Supply & More sources the Z-Flex 2GACKIT0535 and the full range of Z-Flex aluminum and stainless steel chimney liner systems because professional HVAC technicians, plumbers, and mechanical contractors need venting components that ship complete, arrive correctly specified, and perform exactly as listed.
When a gas appliance replacement job calls for a 5-inch, 35-foot aluminum liner rated to UL 1777 standards, the 2GACKIT0535 is the product that meets that specification without compromise. Our inventory supports contractors who need the right liner diameter the same week the boiler or furnace goes in — not waiting on a special order that delays the inspection and the customer's heat.
