• Largely to protect the main masonry units of the chimney — e.g., brick, block, stone and mortar — from deteriorating. A liner keeps out harmful acids and moisture, and acts as a heat buffer. The liner itself may suffer some, but as long as it is, itself, intact, then the exterior masonry can be counted on to do its job.
• A liner also helps to prevent heat transfer, which could threaten wood that is close by (often actually touching the chimney — whereas modern Codes require that combustibles should be no closer than 2 inches).
• A liner may also seal up the exterior masonry that is already in poor condition, and help to prevent harmful combustion gases from escaping into the house.
• Some liners actually strengthen and rebuild the exterior masonry components.
• A tight venting system with a liner, moreover, will perform better than one that has some of the elements of "Swiss Cheese!".

Clay

Clay tile liners — usually found in original construction by masons after 1950. These liner components are usually square or rectangular, but also are available in a round, cylindrical shape. Each tile is 2 feet long and has been fired in a kiln at 1800º. They are pretty durable in the face of acids and heat, but are vulnerable when cool venting gases result in condensation of water-vapor with a resulting wet acid bath. They also are subject, quite easily, to sudden rising or falling temperatures, as found in "chimney fire" occurrences. Masons often fail to use an acid and heat-resistant "refractory" cement between the tile joints, and, furthermore, they frequently do not smooth off the "snots" that squish out at these joints during installation. Tile liners also need to have a minimum ½" of airspace between the tile walls and the main masonry units to account for different rates of expansion (this gap should never be filled). Multiple tile liners in one chimney are supposed to be separated by 4" thick solid masonry "wythe" walls.

Clay tile liner sections often have to be removed to make room for adequately-sized and insulated liner systems during any relining process that takes place after damage.

Stainless Steel Liners — Usually used to retrofit older, unlined chimneys or to repair chimneys whose (tile) liners are damaged or in disrepair.

Types of Stainless Steel Liners:

Flexible, one-piece liners — available in a wide range of shapes and custom lengths — installed by pulling them up or down a chimney using a rope or winch and cable — much more versatile where there are bends or offsets or where narrow passageways require some ovalization. Many flexible liner types are much thicker and more durable than rigid liner pipe, and there are few joints or screws. Stainless steel liners are often insulated for greater safety and performance. They usually have a lifetime warranty.

304 — the common alloy used for wood venting — valuable for providing high heat resistance, particularly in times of chimney fires.

316 — a different alloy whose strong point is acid-resistance, especially appropriate for oil, gas and coal venting — all much more acidic than wood.

AL 294C — an even more acid-resistant alloy, used especially when highly efficient oil and gas appliances result in lots of condensed water vapor, which activates acids even more intensely. Expensive and inappropriate for wood venting.

Shapes of flexliners:
Round is always the best shape for smooth, efficient venting — a vast improvement over squared-off tile liners and preferable to other shapes of stainless steel if room allows.

Ovalized liners allow for passage through some narrow, constricted spots. Stainless steel is malleable enough to be ovalized either at the factory or in the field. Oval drafts better than rectangular, as a general rule.

Square and rectangular liners — usually fashioned from heavier duty stock. Used for special applications where maximum cross-sectional area is needed in a limited space, most often for fireplace venting. More expensive than round and oval shapes.

Gauge and Surface of stainless steel flexliners:

• Lighter weight gauges are most often used for oil and gas (rather than wood) applications where chimney fire heat and burnout are not an issue. These liners are one-ply thick, usually 316 alloy, and have a corrugated wall, which results in a 15% to 20% reduction in flow capacity (because of resistance) for oil and gas applications, compared to smooth-walled alternatives. Easy to work with and relatively inexpensive, however. A two-ply, smooth-wall version is available where flow capacity must be maximized, but this innovative liner (also 316 alloy) is twice as expensive and much more difficult to work with, especially with offsets or constrictions.
• Heavier weight (gauged) liners are usually for wood applications and are of a 304 alloy. They often are of 4 ply construction, extremely rugged and resistant to chimney fire damage. They can be winched up through tight places without tearing apart easily. Their smooth wall construction allows for maximum flow, with minimum resistance and with resulting reduced creosote accumulation. Though much heavier than the lightweights, these liners can be "punished" and shaped to accommodate tough configurations in the field. A 316 alloy version is also available in special circumstances.

Insulation of Stainless Steel Liners (flex)

• Oil and gas liners do not require insulation unless installed on an outside-the-house- chimney in a cold climate. Insulation used in any chimney, however, will maximize draft and minimize troublesome condensation or creosote formation.
  
• Two Options for Insulation:
  1) Foil-backed ceramic wool wrap, either 1/4" thick or 1/2" thick. In most applications, especially wood, the 1/2" thick wool wrap is better, especially since, even in wood venting, it meets what's called "zero-clearance" specifications, which means that there is no problem even if wood or other combustibles are right up against the chimney, contrary to contemporary Code (as is the case in 9 out of 10 new houses and almost all older houses!).
  2) Granular perlite cement mix, available in several brands, but well-known by the Thermix® brand. Mixed with water to a damp consistency, this insulation is poured in around the liner and qualifies for "zero-clearance at 1" thickness. Requires spacing and some finesse to achieve proper and even distribution, but can sometimes be a simpler and less expensive way to achieve appropriate insulation. The firmed-up cement component prevents settling and ensures even performance.
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Poured Masonry Liners

Poured masonry, also known as "cast-in-place", liners involve a proprietary cementitious mix, insulated with fine "perlite" particles. We use a brand of liner mix called Thermocrete™, with a revolutionary quick set ingredient that allows for one-day installation and thus reduced labor costs. Poured masonry liners are "cast-in-place" around a compressed air-filled rubber tube or "former". The mix flows around the former and fills all the nooks and crannies of the flue cavity, thus sealing, strengthening, even rebuilding it from the inside-out. The former is spaced in the flue with stainless steel springs which become imbedded firmly in the mix. Usually a 1" thick wall of Thermocrete™ is desired and is required to meet "zero-clearance" specifications. Much thicker walls may also occur in larger chimneys, resulting in even greater insulation and stability. The advantage of a Thermocrete™ "cast-in-place" liner is that it vastly improves the overall chimney in both structure and performance. It also is appropriate for both high heat (wood) and acidic (oil, gas, coal) appliances — one liner serves all! In a small, compact chimney a poured cement liner may be less expensive than a comparable, insulated stainless steel chimney liner. Like the best stainless steel shapes, it is round for superior performance. On the other hand, it often can be more expensive than stainless or even prohibitive in cost if the flue cavity is very big. It sometimes isn't practical in constrictions or radical offsets. It can only be installed conveniently when the outside temperature is 32° F or higher. It requires specialized and expensive equipment and often more sophistication and more risk than the average small time sweep can handle, so only the more experienced and technically adept companies use this method. In addition, careless application in badly deteriorated flues can result in wall breakthroughs and loss of large quantities of mix, at best, and damage to ceilings, walls, floors and furniture at worst. In the hands of our expert installers, however, Thermocrete™ poured masonry liner is often the best "primo" liner option available. Its longevity is generally acknowledged to be much greater than stainless steel under all circumstances.

Thermocrete™ Spray Process
Ceramic Flue Sealant

Thermocrete™ spray process ceramic flue sealant — the "other Thermocrete™" product is by far the most revolutionary and exciting system on the market for rehabbing old or damaged chimneys. Click on Thermocrete™ for an entire website devoted to this unusual product.

When to Use Thermocrete™ Ceramic:

I) To Repair Damaged Tile Liners

• When thermal shock from a chimney fire has cracked the clay tile liner.
• When extreme acid erosion from oil, gas or coal venting has eaten away a large part of the clay tile liner walls.
  • The Thermocrete™ Process
    • We clean the tile liner interior thoroughly first, as needed
    • Then, working from the roofline, we drop down a spinning spray head, driven by compressed air, and lay down successive thin coats of ceramic mix over a period of several hours, with about a half hour drying/curing time in between coats.
    • The resulting coverage is about 1/4" thick
    • Specifications:
      • Good to 3000°F
      • Impervious to water and acids
      • Repaired tile is as good or better than new
      • Tested to UL 1777 specifications
      • Lifetime warranty
    • Fireplace smoke chambers are usually then enhanced and protected with hand-sprayed Smoktite™ insulated ceramic mix
    • Raincap protection required to validate the warranty
      
      

II) To Repair, Enhance Unlined Brick Chimneys

• This usually means chimneys built before 1950.
• These unlined flues, most often serving fireplaces, frequently are constructed with soft "lime" mortar, before the advent of Portland cement, and the mortar joints are often badly eroded (even all the way through). Basically unlined fireplace flues are not to be trusted, and using them, even only with "small", "occasional" fires, is a risky activity.
• Often the wood framing surrounding unlined chimneys is touching the chimney (contrary to today's codes) and, moreover, has a drastically lowered kindling point due to many years of subjection to hyperdrying from constant moderate heat (a process called "pyrolysis").
  • The Thermocrete™ Process
    • Many old fireplace flues are rectangular and do not lend themselves readily to installation of other types of (round) liners with a large enough capacity for properly venting fireplaces, which have large openings allowing a high volume rush of air and venting gases. Enter Thermocrete™.....!
    • The spraying process is remarkably simple and straightforward and therefore cost effective compared with the complicated alternatives.
    • We clean the flue thoroughly first, as needed.
    • Sometimes we videoscan the flue to pinpoint any observed or suspected holes (e.g., missing bricks or sections of walls).
    • Holes or gaps get repaired. Shaky walls get shored up.
    • We spray Thermocrete™ ceramic flue sealant from the top down, laying down successive coats over several hours with about a half hour drying/curing time in between coats.
    • The resulting coverage is roughly twice the thickness required for tile liners — about 1/2".
    • Extra mix can be sprayed on areas that are particularly weak or vulnerable, in conjuction with other hand-applied solutions.
    • Specifications are the same as described earlier, for tile repair.
    • Fireplace smoke chambers are always sealed, enhanced, reshaped, and protected with a hand-sprayed application of Smoktite™ insulated ceramic mix.
    • Raincap protection is required to validate the lifetime warranty.
    • Thermocrete™ by itself, in an otherwise unlined flue, is not technically classified as a "liner", but it is, by any definition, a solid "lining" inside the old brickwork and as thick and as effective as the clay tile liners mandated as part of current code requirements for chimney construction.
    • Bob and Merrie Warner have used Thermocrete™ to line and seal the three unlined brick fireplace flues in their old 1840's cape home.
    • Thermocrete™ is not appropriate, by itself, for woodstove venting. A woodstove requries an insulated liner tested to UL 1777 zero clearance specifications (usually stainless steel or poured masonry).
    • Unlined brick flues venting gas and oil-fired appliances are usually lined most efficiently and cost effectively with lightweight flexible stainless steel rather than Thermocrete™ ceramic flue sealant although Thermocrete™ may be a necessary option in flue situations with narrow or odd type configurations, or when multiple gas and oil appliances are straining the capacity of the existing flue.
    • Check the Thermocrete™ website at www.thermocreteusa.com, and view their short video.