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Clay Tile vs Stainless Steel Chimney Liners
The liner is the pipe-like passage inside a chimney that carries combustion gases out. Clay tile is the traditional liner in masonry chimneys, and metal liners can be installed inside an existing chimney. Here is how they compare.
What the liner does
The liner (or flue liner) contains hot gases and keeps them away from the brick and the wood framing around the chimney. Metal relining systems are described by manufacturers as an inner pipe set inside the masonry that protects it from heat, corrosion and condensation. For the full set of chimney parts, see parts of a chimney explained.
Clay tile liners
Clay flue tile is the traditional liner in masonry chimneys. Extension-service guidance describes vitrified fire clay tile as able to handle rapid temperature changes and as having a smooth surface that is easy to clean. An ASTM standard (C315) sets acceptance criteria for clay flue liners before they are installed, and a separate practice covers installation. Tiles are stacked and joined with mortar, which means the joints are part of the liner: gaps between tiles or missing mortar can matter as much as a cracked tile.
Stainless steel liners
A stainless liner is a metal pipe installed inside an existing masonry chimney. Manufacturers say these systems are tested to the UL 1777 liner safety standard, are made for different appliance types, and should be confirmed as listed for yours. The pipe diameter is matched to the appliance outlet, and the top is finished with a cap or anchor system. A supplier’s sizing guidance adds that the actual inside dimensions of the existing flue should be measured rather than assumed, because the nominal size of a clay tile can differ from its real size.
| Clay tile | Stainless steel | |
|---|---|---|
| What it is | Fired clay sections joined with mortar | Metal pipe set inside the chimney |
| What an inspection looks for | Cracks, gaps, missing mortar between tiles | Correct size for the appliance, secure connection, finished top |
| Standards | ASTM C315 for the product | Listed to UL 1777 |
Wood, gas and oil
The fuel affects the liner choice. CSIA says that liners serving gas and oil appliances do not need insulation to meet the manufacturer requirements, but liners serving solid-fuel appliances do, and it recommends insulating every liner on a wood-burning appliance. CSIA also notes that gas and oil appliances in exterior chimneys can benefit from insulation. It further warns that an older flue may not suit a modern furnace. If you change fuels or appliances, a Level 2 inspection is called for; see the three inspection levels.
The Department of Energy adds that a chimney should match the appliance outlet size, because an oversized chimney slows the exhaust and can increase creosote buildup, and that a liner should run continuously from the appliance outlet to the chimney top. For how stoves and inserts connect, see fireplace vs insert vs wood stove ventilation and gas vs wood venting basics.
How a problem is found
You cannot judge a liner from the fireplace. A Level 2 inspection includes a visual check of the liner’s interior surfaces and joints, using video scanning or another method, and CSIA procedures list cracks and gaps as findings to report. If a chimney is too dirty, it has to be swept first before the liner can be evaluated. Read more at chimney camera inspection.
Repair or replace?
Options range from repairing a few sections to relining. Manufacturers say a chimney should be cleaned and inspected by a qualified professional before relining, to confirm that the mortar and masonry are sound, and that the appliance maker’s requirements, local codes and permit rules should be followed. The choices, including coating-type repairs, are covered in flue liner repair and HeatShield options. Services: chimney liners and HeatShield flue repair. For a documented example, see our Jersey City project, where a Level 2 inspection led to a new liner and crown repair.
Frequently asked questions
Is a clay liner bad?
No. A sound clay liner that suits the appliance can do its job. The issue is condition, which needs an inspection to judge.
Do I need a new liner if I add an insert or stove?
The liner has to suit the new appliance. This is checked before installation; see the venting guide linked above.
Does a liner need to be insulated?
For wood, CSIA recommends it. For gas and oil, it depends on the manufacturer’s requirements.
Next step
Request a visit or call (862) 225-6529 for a liner assessment. We are a registered (NJ HIC #13VH14312300) and insured New Jersey home improvement contractor.
Sources
- CSIA: Homeowner Resources FAQ (liner insulation for solid fuel vs gas and oil; older flues and modern furnaces)
- CSIA: The Three Levels of Chimney Inspection (Level 2 required for fuel or appliance changes and relining; liner interior check)
- CSIA: Level 2 Masonry Chimney inspection procedure (cracks and gaps in liner reported)
- DuraVent relining systems technical catalog (general: purpose of a liner, UL 1777, appliance types, inspect before relining)
- Rockford Chimney Supply: liner measurement guide (measure actual flue dimensions; nominal tile sizes vary)
- ASTM C315 (scope: acceptance criteria for clay flue liners; installation covered separately)
- University of Missouri Extension, G1732 (vitrified clay flue tile properties)
- U.S. Department of Energy: Wood and Pellet Heating (chimney matched to appliance outlet; continuous liner)