Masonry Chimney Lining and Safety

Keep your masonry chimney safe to use, and learn about two chimney relining installation methods.

| September/October 1983

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 Wood Stove Safety, 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, 1982).

The subject of this article, then, is aging and/or unsafe masonry chimneys, and what you can do if you're faced with the task of repairing a masonry chimney. 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.

Clean and Inspect the Chimney Regularly

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).

Relining a Chimney

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!

12/10/2007 8:37:08 PM

I would like to get my Chimney re-lined with either a 5" to 6" Ventinox system. I am reading everywhere that the cost is around $15 -$20 dollars per foot for the Ventinox. I am also reading that the total price will be around $30.00 to $40.00 dollars per foot. I have a 42 foot run. I am willing to pay the $40.00 per foot and even a little more. However the companies around here are quoting me more than double that price. Can you give me any recommendations and a quality company that will do a job for a resonable price. I am located in Shelton Connecticut which is an hour north of NYC, or an hour south of Hartford. I would appreciate your imput or if you know of a reputable fair company.

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