Flue Pipe Durability

A reader who uses an occasional chimney fire to clear creosote from his woodstove flue pipe asks how long he can expect the pipe to last.
September/October 1984
http://www.motherearthnews.com/homesteading-and-livestock/flue-pipe-zmaz84sozraw.aspx
With proper care, a flue pipe made of good single-wall steel should last many years.


Photo by Fotolia/vlorzor

I use a German Weso “tile oven” woodstove for night and sunless-day heating in my passive solar home. The design of the flue pipe causes it to be exposed to the house’s interior (it’s attached to the back side of a Trombe wall) for about 20 feet until it exists through the ceiling into, and out of, an exterior chase. When I built the home three years ago, I installed quality, 24-gauge flue pipe. I burn at least one very hot fire each day to get rid of any creosote deposits (and I’ve never had much of a problem with creosote accumulations). A thermometer is magnetically attached to the flue about three feet above the rear exit of the stove, and when I burn my first “hot” fire each morning, the thermometer always registers from 600 degrees Fahrenheit to 750 degrees Fahrenheit, while steady-state heating registers from 250 degrees Fahrenheit to 350 degrees Fahrenheit. 

My question concerns the safety and life expectancy of the flue pipe. How long can the pipe be expected to last (especially at the hot 90-degree elbow at the stove’s rear exit) if used daily for a four- to five-month heating season? 

No one answer is applicable to all situations. However, in most cases, good single-wall steel stove pipe such as yours will last for many years.

I am aware of three conditions that can cause premature failure of stove pipe. They are [1] corrosion from acidic condensed flue gases (your flue temperatures appear to be high enough to prevent water condensation); [2] the presence of corrosive gases resulting from burning household trash (some plastics, when burned, yield hydrochloric and hydrofluoric acids); and [3] excessive temperature (a glowing pipe will have a much-reduced life expectancy). And, if you live near the coast, humid weather and saltwater spray can also accelerate corrosion of the stove pipe.

I’ve known cases in which the stove pipe needed to be replaced twice in one season, but on the other hand, I suspect that most quality stove pipe will last for years. If you occasionally inspect the exterior of the pipe, both visually and by tapping it with the handle end of a screwdriver, you’ll most likely discover any weaknesses in the metal before they become a hazard. An annual inspection and cleaning by a chimney sweep will also help to reveal any faults in the pipe.

Jay Shelton is the director of Shelton Energy Research.