Prefab Chimney System Characteristics

        Prefab chimney systems cannot be used the same way as a masonry chimney system.   The average person doesn't even know if they have a prefab or a masonry fireplace.

There are important things that you as a homeowner need to know about prefab systems:

Prefab Chimney Firebox
        The firebox, where you make the fire, is built out of steel and typically has four walls (two sides, a back, and a floor)  of what we call refractory panels inside the box.   These panels are cast in molds out of a refractory cement and look like bricks.   Their purpose is to reduce the heat to the firebox.
Cracked Wall Panel
        The refractory panels can easily crack and are extremely expensive to replace.   Cracks in the panels can also cause a potentially dangerous situation when they have lost their insulating ability and may transfer heat to combustible materials.   Most of the fireplace manufacturers recommend replacing a panel if you can fit the thickness of a dime inside the crack.

Damaged Refractory Panel
        The main cause for cracks developing is having fire that is too big or too hot.   We recommend that you should limit the size of your fires to either ONE prefabricated log (i.e. Duraflame or Pine Mountain),  or just 2 to 3 small pieces of wood at one time.
        Unlike a masonry chimney, a prefab chimney system carries a UL Listing, and is actually considered an appliance.   Prefabs can not be modified in any way or it will void the UL Listing, and any warranty.   The Prefab Refractory Wall Replacement  page shows the replacement of the refractory panels in a prefab fireplace.
        The generic "universal refractories"  are made by outside companies and are cut by the installer to fit as replacement panels.

        On most prefab systems, there is a flat metal cover on the top that the chimney cap which attaches to what is called the chase cover.   Sometimes rain may leak inside the chase cover, one sign would be if you hear water dripping on metal inside the wall by the fireplace during or after it rains.   This must be addressed immediately so that the chase cover can be replaced.   If you wait too long, the water will rust out the system and the entire system will need to be replaced.

Examples of Potential Prefab Problems...

Replacing a chimney cap with a non-factory unlisted cap.   The flue pipe in a prefab system generally consists of an inner pipe, an air space and an outer pipe.   The air space in between the pipes is there to cool the system, using the wrong cap can inhibit this cooling and allow the system to overheat which could be a potential fire hazard.
Installing glass doors on a prefab system that was not designed specifically for that fireplace model  could overheat the system since the doors may cover up the air vents inside the firebox that will normally draw in cool air.
Using a non-factory shroud or decorative surround around the chimney cap at the top  might restrict the chimney system's ability to properly vent.   These modifications can even make it impossible to clean the top area of the chimney when sweeping or be able to perform a visual inspection from the top.
How a prefab system is maintained can make a huge difference in how long the system will last and how safe it is when used.   Rust can be a major problem  since the metal becomes thin and weak, and can even rust through.   Of course this problem seems to most often occur in areas of the system that see the highest heat such as around the damper area, in the flue pipe and chimney cap.   There is a lot of rust in systems in parts of the county close to the ocean.   This will prematurely require replacing the entire system.
If something looks a little strange, it is strongly recommended to have the chimney system checked out by a professional chimney sweep to avoid any problems.
        Most prefab systems only have a life span of about 15 - 30 years (partly depending on how close it is to the coast), whereas masonry chimneys built today could last upwards to one hundred years or more.   Many of the prefab systems that are in homes built in the 1970's here in San Diego & Riverside counties are getting to the end of their life.   It's very critical to have your system maintained by a professional chimney sweep to avoid as much risk as possible of a costly fire.

To return to Prefab Chimneys  Main Page.

To go to the Prefab Refractory Wall Replacement  Page.


        If you would like to schedule an appointment with our company the following TIPS  will help assist in the completion of your scheduled appointment.

(Source:   CSIA, NCSG, CCP, GSCSG, NFI, PERC, NFPA, PFI, AGA, HPBA, FIRES, USFA, Cal/OSHA )   External Links

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