RELINING MASONRY CHIMNEYS

Enlarge Image Image Gallery Flames from a chimney fire can generate temperature that exceed 2000?F. [2] Installing the weather-sealing, stainless steel cap on a Ventinox relined chimney.[3] The Ventinox system usually uses a stainless steel baseplate inside the smoke chamber. [4] To reline a chimney with the Insulcrete system, a bladder is inserted into the flue and inflated with an air compressor.

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

Issue # 83 - September/October 1983 A woodstove is just one part of any solid-fuel combustion system, and there's a strong possibility that another component may be a weak—and dangerous—link.

You may be surprised to learn that most wood-heating industry experts agree that faulty appliances are seldom the cause of home fires these days. Rather, most woodburning-related tragedies today are the result of either improper installation or poorly maintained flue systems. Back in MOTHER NO. 61 (see "Wood Stove Safety" on page 72 of that issue), we covered installation practices in some detail ... and if you're at all unsure about the safety of your heater's location and connections, we strongly suggest that you refer to that feature or to an authoritative reference book (such as Jay Shelton's Solid Fuels Encyclopedia, Garden Way, $12.95).

The subject of this article, then, is aging and/or unsafe masonry chimneys ... and what Yon can do if you're faced with the task of repairing one. Though folk wisdom often seems to imply that brick chimneys are the best, such flues are all too often unsuited (and/or unsafe) for use with an add-on wood burner. Very few masonry chimneys, you see, have been (or are now being) built to suit the gas flow rates common to controlled combustion ("airtight") heaters, and the typically too-large masonry flues reduce draft and increase creosote buildup. Worse yet, many, older chimneys lack any sort of liner to protect the brickwork from the extreme temperatures that can be generated by a chimney fire (such blazes can exceed 2000'F). And even flues that are lined with tile may have deteriorated under the abuse caused by chimney fires, to the point where smoke (or flames) can escape into the house through cracks. As you can see, then, masonry chimneys often actually produce conditions that can lead to danger . . . by virtue of their very design.

Nonetheless, no matter what sort of chimney you're using with your woodstove, you should definitely have the system cleaned and inspected regularly. Of course, you may want to leave this vital (and somewhat unpleasant) task to a qualified sweep, but-with a little bit of study and a steady pair of feet on the rooftop-there's no reason why You can't learn to do this job.

As you familiarize yourself with your woodburner's ventilating system, one of the first things you'll have to learn is the size of the chimney brush needed to clean it properly. Once you've determined that dimension, you can compare your flue size directly (if' it's round) against the stovepipe diameter recommended by your heater's manufacturer, or calculate the cross-sectional area of a rectangular stack for comparison with that figure. When checking the suitability of your chimney, bear in mind how much even a small increase in size influences capacity: An eight-inch-diameter chimney, for example, has almost twice as much cross-sectional area as does a six-inch one. Thus, what might seem like a small deviation from recommended procedure could make a big difference in performance and safety.

Once you (or your sweep) have cleaned the walls of the flue, the lining should be checked for cracks or holes, and the mortar joints between the tile sections should be inspected for soundness. Most professionals do this by using a mirror to reflect sunlight down into the chimney, but a trouble light may be helpful on cloudy days (and when inspecting chimneys with bends).

Should the examination turn up deficiencies in the size or condition of the chimney, there are basically only two things you can do: You can tear it down and build a safe, properly sized one, or you can have your existing flue relined. There are a couple of good reasons for taking the second approach: For one thing, relining a chimney costs approximately a third of what a mason would likely charge to disassemble an old one and build a new stack in its place ... and a relined chimney may actually end up being safer and more durable than a new tile-lined one!

In the following paragraphs, we're going to describe two methods of lining an existing masonry chimney. Both systems have their strengths and weaknesses-which we'll try to point out-and neither is exactly inexpensive. However, each approach can produce a chimney that, when used in conjunction with a controlled-combustion woodburner, is essentially better than even a new brick chimney. We'll be featuring a pair of specific systems that we've seen in action, and will list other manufacturers of similar products at the end of the article. Of course, the fact that we've chosen to show you the Insulcrete and Ventinox reliners doesn't mean that we necessarily judge them to be superior to all other products. From personal experience, we do have confidence in their systems, though ... and we're very grateful to Pete Luter (president of the North Carolina Guild of Professional Chimney Sweeps and a reliner himself, out of the Roanoke Rapids, North Carolina shop called Countryside) for leading us to them.

VENTINOX STAINLESS STEEL

In the past, many people who've found their chimneys to be incapable of providing acceptable draft for a woodstove have resorted to stringing stovepipe up the flue. And, though the practice usually has accomplished its goal, quite often the owners have been surprised to find that creosote built up inside the metal pipe at an alarming rate. Without insulation around the steel tubing, heat is lost from the smoke so quickly that the products of incomplete combustion readily condense on the walls of the flue. Furthermore, if the material used for such a simple relining is merely galvanized stovepipe, the system will deteriorate very quickly.

On the other hand, existing chimneys that have been relined with quality stainless steel pipe have a far better track record for longevity, but still suffer from rapid creosote deposition ... unless they're insulated. Unfortunately, running a factory-built double- or triple-wall chimney up a masonry flue is cumbersome and expensive (these systems can cost as much as $55 per foot). This method also does nothing to strengthen a weak brick stack, and can be downright impossible if there are any significant bends present in the existing flue.

However, a system commonly used by the Swiss avoids such problems by employing a high-grade, flexible stainless steel liner (to accommodate turns) with a fill of insulation (for good draft and low creosote deposition) or-when necessary for strength--a mix of insulation and masonry cement. The Ventinox relining method (as it's called) came to the U.S. less than a decade ago, when a transplanted Austrian, Martin Wawrla, was faced with the job of relining four existing chimneys while restoring his Albany, New York home. After coating the inside of one flue with refractory cement, a procedure that involved opening an access hole every few feet, Martin decided to track down the owners of the relining system he'd seen so often in Europe. By working through the Swiss office of Ventinox, he ended up proposing to the U.S. division of the company, American Boa, that it bring the European system to this country. As a result, Martin is now project manager of American Boa's growing chimney relining business.

The Ventinox liner is made from a continuous band of 33-gauge 321 stainless steel that is corrugated, rolled in a spiral, and then bound together by a computer-controlled electric welder. The corrugated spiral helps give the comparatively thin material strength and reduces problems with thermal expansion (which has been known to lift the top right off a chimney relined with solidly mounted standard stovepipe). In addition, 321 stainless is perhaps the steel alloy that's most resistant to the corrosive environment in a woodburner's chimney, and the company guarantees its product for ten years.

Of course, other stainless alloys may last as long as 321 does in most environments, but the strain imposed by a chimney fire can eventually be the undoing of lesser metals. You see, once many corrosion-resistant steels have been heated to above 2000'F, the chromium in the metal (which prevents corrosion) may begin to lose its bond with the other elements ... and intergranular deterioration can then begin. To date, Ventinox is the only stainless reliner that's been tested to both Underwriters Laboratories basic (UL 103) and high-temperature (2100°F) standards.

Installing Ventinox is a straightforward job, and trained crews have been known to do a basic chimney in just three hours. The procedure consists of installing a baseplate, with a hole to fit the diameter of the liner (Ventinox is available in six-, seven-, eight-, and ten-inch sizes for residential applications), on the smoke shelf above the fireplace ... threading the one-piece tube down the chimney, engaging it into the baseplate, and centering it with spacers ... filling the area around the liner with the appropriate insulative mixture ... and capping the relined flue.

RSS | Comments | E-mail | Print