Chimney Liner Comparison: Clay Tile vs. Stainless Steel vs. Cast-in-Place
The three main types of chimney liner compared side by side: what each is, what it suits, and where it falls short.
What a chimney liner does
The liner is the inner surface of the flue. It has three jobs: keep heat away from the wood framing around the chimney, keep corrosive flue gases off the brick and mortar, and give the appliance a flue of the right size so it drafts properly. A chimney with a cracked, missing or wrongly sized liner fails at one or more of these.
Side-by-side comparison
Clay tile is cheapest in new construction, stainless steel is the most adaptable for relining, and cast-in-place costs the most but also strengthens the chimney.
| Clay tile | Stainless steel | Cast-in-place | |
|---|---|---|---|
| What it is | Fired clay sections stacked and mortared inside the chimney as it is built | Rigid or flexible stainless pipe lowered down the existing flue, usually insulated | Cement-like mix pumped in around a former to make a seamless round flue |
| Best suited to | Open wood-burning fireplaces in a chimney built with it | Wood stoves and inserts, gas and oil appliances, and relining damaged clay flues | Old or structurally weak chimneys, especially unlined ones |
| Typical lifespan | Decades if kept dry and never overheated | Long, if the right alloy is used for the fuel | Very long; it becomes part of the chimney |
| Relative cost | Lowest in new construction; costly to replace later because tiles must be broken out | Middle | Highest |
| Main weakness | Cracks under sudden heat, such as a chimney fire; joints erode; poor with the cool, moist exhaust of modern gas appliances | Reduces the flue size slightly; the wrong alloy will corrode | Specialist installation; cannot easily be undone |
| Can it be resized for a new appliance? | No | Yes, that is its main advantage | Yes, at installation |
Clay tile liners
Most masonry chimneys built in the last hundred years have clay tile liners, and in a well-kept chimney serving an open fireplace they do the job for a long time. Their weakness is thermal shock. Clay tiles do not expand evenly when heated fast, so a chimney fire can crack several in seconds. The mortar joints between tiles also wear away, leaving gaps.
Clay is also a poor match for modern, efficient gas furnaces and water heaters. Their exhaust is cooler and wetter, it condenses on the tile, and the acidic moisture eats the clay and mortar.
Stainless steel liners
A stainless liner is a continuous pipe from the appliance to the top of the chimney. Because it comes in many diameters, it can be matched exactly to a stove, insert or furnace, which is something clay cannot do after the chimney is built. Insulating the liner keeps the flue gases warm, which improves draft and reduces creosote and condensation.
The alloy has to suit the fuel. Liners sold for wood-burning are made from different stainless alloys than those made for the acidic condensate of high-efficiency gas appliances. Aluminum liners exist too, but they are only suitable for certain gas appliances and never for wood.
Cast-in-place liners
For a cast-in-place liner, an inflatable or removable former is centered in the chimney and a lightweight, heat-resistant cement mix is pumped around it. When the former comes out, what remains is a smooth, seamless, insulated flue bonded to the inside of the chimney. It adds strength, which makes it a good answer for old chimneys with weak mortar. It costs the most and needs a specialist crew.
Our opinion: which liner for which situation
In our opinion, keep a sound clay liner, reline with stainless steel when the clay fails or the appliance changes, and consider cast-in-place for a structurally weak chimney.
- Clay liner in good condition, open fireplace: leave it and keep inspecting it.
- A few cracked tiles or open joints: ask about repair or resurfacing before full relining.
- Badly damaged clay liner, or after a chimney fire: stainless steel relining.
- Adding a wood stove, insert or new gas furnace: a stainless liner sized to that appliance.
- Old chimney with weak structure or no liner at all: consider cast-in-place.
This is our view, not a rule, and the condition of your particular chimney decides it. A Level 2 chimney inspection with a camera shows what state the current liner is in. For other parts of the chimney, see the chimney anatomy diagram, and for the work itself, chimney repair.
Sources
- National Fire Protection Association, NFPA 211, on chimney lining and flue sizing.
- Chimney Safety Institute of America, homeowner resources on chimney liners.
Common questions
How do I know if my chimney liner needs replacing?
Signs include pieces of clay tile in the firebox, a chimney fire, visible cracks or gaps on a camera inspection, or a new appliance that the existing flue is the wrong size for. A Level 2 inspection with a camera confirms it.
How long does a stainless steel chimney liner last?
A stainless liner of the correct alloy for the fuel, properly installed and swept regularly, typically lasts for decades. Using the wrong alloy, for example a wood-rated liner on a condensing gas appliance, shortens that sharply. Insulating the liner and keeping the cap in good order both help it last.
Can a chimney be used without a liner?
It should not be. An unlined chimney lets heat reach nearby framing and lets acidic flue gases attack the mortar. Building codes have required liners in new masonry chimneys for many decades, and unlined chimneys should be lined before use.
What is a cast-in-place chimney liner?
A cast-in-place liner is a cement-like lining pumped into the chimney around a removable former, leaving a smooth, seamless, insulated flue. It bonds to the inside of the chimney and strengthens it, which suits old or unlined chimneys. It is the most expensive of the three liner types.
Are clay tile liners suitable for gas furnaces?
Often not, with modern furnaces. High-efficiency gas appliances produce cooler, wetter exhaust that condenses on clay tile, and the acidic moisture damages the tile and mortar. A stainless steel or aluminum liner sized to the appliance is the usual answer.