Prefab Chimneys

(aka Zero Clearance Fireplaces)

        Prefab fireplace/chimney systems generally consist of a metal firebox with either metal or refractory panels on the sides, back and floor, a dual or triple wall metal flue pipe and a chimney termination cap.   They are typically found in homes built during and after the 1970's or during a remodel.   The components have been tested by the fireplace manufacturer and carry a UL listing.   For safety and liability reasons these systems should never be modified.

        While this page provides very good information about the prefab chimney systems, we strongly recommend going to some of our more detailed pages about prefabs, such as the Prefab Chimney Characteristics  page and the Prefab Refractory Panel Replacement  page that shows a complete set of refractories being replaced in a prefab fireplace.

        Shown below are the two types of prefab fireplace installations: one with a surrounding housing called a "chase",  and the other with the metal flue pipe extending up above the roofline...

Exploded View Prefab Chimney Exploded View Prefab Chimney
        Check out our replacement of the refractory panels in a prefab fireplace.
External Chimney Flue
Above is an external chimney flue.
        A chimney flue is the passageway inside the chimney that the smoke, heat and gases travel through before exhausting to the outside.   It is important that the chimney flue be well insulated with an adequate lining material since it can be exposed to very high temperatures--especially in the case of a chimney fire.   A pre-fab chimney is a metal pipe that is housed inside a wood box, usually covered with siding or stucco.   Pre-fab chimneys started being used around the 1970's, so if your house is much older than that you probably have a masonry chimney.

        Like other parts of your home, chimneys and fireplaces require some maintenance, inspections and occasional repairs.   Using a professional chimney sweep will assure that your chimney has been fixed or cleaned properly and safely.   See the diagram below and read the descriptions of the chimney, how the parts work together and some of the maintenance and repairs chimneys require.  

        In matters of fire safety the best way to assure your safety is to have a professional chimney sweep inspect your chimney.   The diagram and explanations here are to help you know when to call the chimney sweep and to understand the work the chimney sweep is performing.

Pre-Fab Chimney Diagram
        A pre-fab chimney begins with the firebox.   This is the box in the fireplace inside your home where you build the fire.   The firebox is where the chimney sweep begins your chimney inspection and where the chimney sweep cleans the chimney from.   Just above the firebox is the chimney's damper.   The damper is like a door between your fireplace and your chimney flue that you open when you have a fire to let the smoke escape and close when you're done to keep the elements out and to keep your heating and air-conditioning in.   It is smart to have a chimney sweep inspect your damper to make sure it is not costing you money.   Above the chimney's damper and on top of the fireplace is the chimney's air cooled flue.   This chimney flue is made of two pipes, one inside the other.   The inner pipe is how the smoke escapes from the firebox.   It's the smoke that distributes the soot in this flue and this is what the chimney sweep brushes out when the chimney sweep cleans your chimney.   You should have your chimney cleaned regularly by a chimney sweep to prevent a fire in your chimney flue.   A fire in the chimney flue can lead to expensive repairs or worse, a house fire.   The outer pipe of the chimney's air cooled flue takes in fresh air from the outside and cools the inner pipe.   It is important to have a professional chimney sweep with knowledge of prefab chimney systems handle your chimney repairs to assure that they know how to keep air flow in this outer chimney flue pipe.   The entire mechanism is housed inside a wood box called the chimney's chase.   The outside of the chimney's chase usually has stucco or siding on it.   On the top of the chimney's chase is the chase cover which functions as a roof for the chase.   The chase cover looks like a cake pan turned upside down with a hole in the center that the chimney's flue goes through.   Some people refer to the chase cover as a chimney's flashing.   Both terms are correct.   On top of the chimney flue is the chimney cap.   The chimney cap protects the flue and keeps the elements out while allowing smoke to escape from the house.   The chimney cap has an animal guard, so you don't get any unwanted visitors in your home.   The chimney cap has a spark arrestor on top that keeps embers from landing on your roof or in your foliage.   spark arrestor, when actually it is just a part of a chimney cap.   Chimney caps are also referred to as a spark arrestor or termination cap.   All these terms are correct.   Be careful that you have the right kind of chimney cap installed on a pre-fab chimney.   If the outer pipe of the chimney flue is not able to get enough fresh air the inner chimney flue can get too hot and cause a fire.   We recommend you use a professional chimney sweep for these repairs to assure that the installation does not interfere with the air flow.   A common chimney repair for pre-fab chimneys is when the chimney caps and chimney chase covers rust and corrode and then leak water in your home.   This can rust out the chimney flue, making it unsafe, cause wood rot and mold that require expensive repairs.   The best thing is to have a chimney sweep inspect your chimney every year to make sure you don't have rust forming.   If there is rust Apex Duct And Chimney Cleaning uses aluminum and stainless steel chimney caps and chimney chase covers that will not rust so we can give them a lifetime guarantee not to rust. Lastly, there is a small vent going from the firebox to outside the chimney chase. This is the chimney's fresh air return, it fuels the fire with the oxygen it needs to burn and keeps smoke from coming back into the house.   Not all pre-fab chimneys have a fresh air return.   Note, some pre-fab chimneys in the older neighborhoods do not have a chase and are contained within your walls and just have a pipe coming out of the roof with a cap on top.   There is no chase cover as there is no chimney chase.   If you have any questions about your pre-fab chimney you can Contact Us and we will be happy to answer your questions.


Prefab fireplaces are not designed to handle extremely high temperatures.   It is recommended to only burn 2 or 3 small pieces of wood at a time, or 1 manufactured log at a time, such as Duraflame or Pine Mountain.
If the refractory panels do crack, and the thickness of the crack is the thickness of a dime or more it should be replaced.   Many manufacturers will only sell the panels as a complete set (backwall, 2 sidewalls, floor panel, and possibly ash lip).
Aftermarket nonfactory glass doors are not recommended on a prefab fireplace.   They may cause the system to overheat, and the system was not tested and approved with them any warranty may be void.
A prefabricated fireplace are ones that have been manufactured in a factory and installed at a home or job site.   Many of these are ventless.   This allows the user to burn a gas fire without the need to vent any fumes to the outside of the home.   These fireplaces are typically installed inside of an existing fireplace, while the majority of units are built now for new construction or remodeled rooms.
Most prefabricated fireplaces work with manufactured gas burning logs.   These logs resemble natural logs, but they are ceramic and equipped with a gas line running through them.   These gas lines also feature tiny gas holes that simulate flames running along the length of the log set.   Vented fireplaces uses different logs than ventless versions.
Installing a prefabricated fireplace requires the construction of a surround.   The opening of a surround is designed to allow the metal fireplace to slide into place and attach through the flange on the fireplace.   Screws that are run through the metal flange of the fireplace and into the wood of the surround efficiently mount the unit in place.   Gas and electric lines run to the fireplace inside of the surround.
A lot of these fireplaces are designed with blowers.   By installing small electric blowers inside the fireplace, the heat generated from burning the gas logs can be blown into a room.   This creates not only the peaceful visual pleasure of a fireplace, but the warming qualities as well.
On the vented prefab fireplace models, the gas fumes are directed out of the home with a chimney.   The chimney is often a fa├žade of wood construction surrounding galvanized stove pipe.   The galvanized pipe is typically multi-layered and is run through the false chimney along the exterior wall of the home and vented near the peak of the roof line.   In homes with an actual working chimney, the fireplace is routed to the chimney with the multi-layer pipe.
Prefab fireplace designs offer the best of both worlds to homeowners - the safety and convenience of a gas fireplace that is complete with safety features along with the romance and atmosphere of a wood burning fireplace.   Cleaning of ashes and soot are replaced with dusting and polishing the metal construction.   A multitude of mantle designs are available to maximize the visual impact of the fireplace inside of a home.

Alteration Options

The expense and labor involved in a prefab fireplace replacement may lead you to consider a conversion or alteration of your fireplace.  CAUTION: ABSOLUTELY DO NOT PUT GAS LOGS into a damaged or deteriorated wood burning fireplace.   Vented gas logs require the fireplace and chimney to be suitable for use with wood; if it's not safe to burn wood, it's NOT SAFE to use with gas logs, either!
A GAS INSERT is a stove that inserts into your fireplace and may be a practical option to tearing out the fireplace that's already there.   As some gas inserts carry a dual listing as either an insert or a complete fireplace system (such as the Windsor), inserting it into a metal fireplace should not cause fire safety concerns.   Again, you'll have the convenience of burning gas and it's comparatively inexpensive versus replacement of the fireplace.
An ELECTRIC INSERT is a very inexpensive option.   An electric fireplace is uniquely capable of offering you flames with no heat so you can have a romantic fire in the summer, or use with the heater when the weather turns cooler.   This at least provides you the ambiance of a "fire" with no need to tear anything out, and is an option many of our customers have chosen in recent years.


Only have a qualified professional hearth installer who is NFI certified do the installation.   We HIGHLY recommend NOT making this a DIY project!   Most city codes require installation to be completed by a licensed installer.   One small mistake can result in a house fire, so it is not worth trying to do this yourself or having a builder who is NOT  NFI certified do the installation.   Do a search on the NFI website to find a local certified installer.
Never have any part of the system replaced with anything other than those that have been made and approved by the manufacturer to be installed on your specific system.   This applies to chimney caps, refractories, glass doors, and chimney flue pipe.   For more information on Prefab fireplaces, check out these other pages.

Primary Safety Concerns

Improper Installation It is by far the most common cause of failure.   If clearances to combustibles weren't closely followed, along with exact configurations of the metal chimney venting, the ignition temperature of the wood and sheet rock nearby the fireplace can be reduced over time, a process called "pyrolysis".
Improper Use Keep in mind, a prefabricated wood fireplace is designed for occasional, recreational type fires.   Don't over fire by building large, hot fires or use them for hours and hours on end to try and heat.   By and large, these fireplaces are considered decorative appliances and are not designed to provide substantial heat.
Field Modifications It is extremely inadvisable to install a stove (such as a wood burning insert) into a prefab fireplace.   Use caution when attempting to install after-market glass doors, too, that may interfere with the fireplace's design to circulate and disperse heat properly.   Never attempt a renovation project that covers louvers or air channels that were designed to help keep the fireplace properly cooled.
Inadequate Maintenance It's imperative that you have your chimney checked annually and the chimney swept when needed.   One of the most important aspects of the inspection is the chimney termination on your roof.   The flashing surrounding the chimney pipe easily becomes deteriorated over the years, contributing to water damage, rain leaks and rotting wood.   Deteriorated flashing can also allow birds and animals to enter the chimney chase (the framed "wooden" chimney area) where varmints often build flammable nests adjacent to the pipe.
If you're advised of a safety or performance issue, DO NOT use your fireplace.   It's time to investigate replacement or alteration

Prefab Chimney Characteristics

Prefab Refractory Panel Replacement


        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

Website Vistors As Of:  January 17, 2021
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