Prefab Chimneys — How Are They Different From Masonry Chimneys & How Are They The Same?

Also known as factory-built chimneys, prefabricated fireplaces, or class A chimneys, prefab chimneys are common appliances around town. With proper maintenance and proper usage, a factory-built fireplace and chimney can last a lifetime. However, there are key differences between prefab chimneys and masonry chimneys.

#1 Material

Masonry chimneys are chimneys that are built on site, brick by brick, or stone by stone. Prefab chimneys, on the other hand, are constructed and tested in the factory. Instead of being built in your home or business, they’re installed.

#2 Lifespan

Unlike masonry chimneys, prefab fireplace systems have a serviceable life and eventually just plain wear out. Models go out of production and manufacturers go out of business. And since every component in the chimney system is UL tested and listed to work together, when damage occurs, not just any part can be used as a replacement. A factory-built unit will reach the end of its useful life when repair of the unit is no longer possible, particularly if the components that are necessary to maintain the listing are no longer available.

Aside from general wear and tear, there are some other things that can contribute to a shortened lifespan for your prefab chimney system. Most prefab fireplaces are tested and listed as decorative heating appliances and will not stand up to the same usage as masonry chimneys. If you use your factory-built like you would a masonry chimney, it may not last even 5 years.

Even though they’re tested to UL standards, severe overfiring and chimney fires will often badly damage these units, sometimes to the point of replacement. What is overfiring?

Overfiring is when you burn fires that are hotter than the temperatures your prefab chimney or fireplace is designed to handle. This can be the result of using too much wood at once or allowing the stove or fireplace to get too much oxygen. Some other things that can result in overfiring:

  • burning kiln-dried mill ends
  • burning cardboard
  • burning paper
  • burning treated lumber
  • burning rubber
  • burning styrofoam
  • burning plastic

In addition to avoiding the things above, as an extra precaution you can have a thermometer installed in the “hot spot” of your stove or fireplace, so you’ll always know when you’re headed for the danger zone.

Prefab Chimney with Chase

Prefab Chimney with Chase

Prefab Chimney with No Chase

Prefab Chimney with No Chase

Prefab Chimneys Need Inspections & Sweepings, Too!

So how can you tell if your factory-built chimney is safe for use? Like you would with a masonry chimney, schedule an annual inspection and sweeping. I’ll look at every component and make sure things are still working as they should be.

If not, I may recommend a new class A chimney that’s UL listed to the 103HT standard, which requires, among other tests, that the chimney withstand three 10-minute chimney fires at 2100 degrees F (1150 degrees C).

Because I care about my customers and their safety, I install only the very best prefab chimneys, Industrial Chimney Company (ICC) stainless steel chimneys. These chimneys exceed the UL 103HT standard and are listed to the more stringent Canadian standard, which, among other tests, requires the chimney to withstand three 30-minute chimney fires at 2100 degrees F (1150 degrees C).

Have questions about prefab chimneys or need to have yours inspected, swept, repaired, or replaced? Check out my page on chimneys & stove pipes and give me a call at 208-550-8474 — or click here to request an appointment.


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