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Is It Time To Replace Your Wood Burning Prefabricated Fireplace?

Prefabricated metal fireplaces became popular in the 1970s as an inexpensive alternative to building a masonry fireplace. They were targeted to homeowners who desired to have an open burning decorative fire on an occasional basis. They were NOT intended to be a primary heating source or to have a wood burning insert installed into them. 

Along came the oil shortages of the late 1970s and many homeowners tried to push the limits of their capability; they tried to stuff them full of wood to create more heat and burned them continuously for days or weeks at a time, hoping to provide supplemental heat or reduce home heating oil bills. 

Whether you’re the original owner of one of these older homes or have recently moved into one, it’s essential that you have the prefabricated wood burning fireplace and chimney thoroughly inspected every year, especially since many of them were overfired in earlier decades, presenting fire safety issues.

Of great concern is the fact that older models are now approaching 30 to 50 years old and causing a considerable number of house fires. While a masonry fireplace may last as long as the house stands, a prefab wood burning fireplace is considered (by industry standards) to have a lifespan of 10 to 30 years.

Prefab decorative wood burning fireplaces are made of relatively light-weight metal; precast “firebrick” style panels and air chambers. That is all that separates the fire from the combustible framing in your home’s walls. This photo shows a fireplace installation before sheetrock has been installed. Isn’t it kind of scary that framed walls are actually that close to a wood fire? Too many really are made like a cheap tin can and installed against the walls of your home, often with improper clearances and lacking required air spaces meant to help keep them cool when burning. Unfortunately, there’s a lot that can go wrong.

prefabricated wood burning fireplace surrounded by wood beamsEven when installed correctly – meeting the manufacturers’ minimum clearances to combustibles – metal wood burning fireplaces just were not designed for heavy-duty use for decade after decade. Time and age are beginning to show on these old fireplaces, and tragically house fires are now occurring on a frequent basis.

photo courtesy

Primary Safety Concerns

*Improper Installation is the number one cause of house fires from a prefab wood fireplace.  If clearances to combustibles weren’t closely followed (along with exact configurations of the metal chimney venting) the ignition temperature of the wood and sheetrock adjacent to the fireplace system can be reduced over time.  This process is called “pyrolysis” and can char the wood and then cause ignition of the framing. fireman in suit looking through damaged house


*Improper Use Remember, prefabricated wood burning fireplaces are designed for occasional, recreational type fires. Don’t over fire by building large, intense hot fires or use them continuously to try and heat your home. By and large, these fireplaces are considered decorative appliances and are simply not designed to provide substantial heat.


*Field Modifications It is extremely inadvisable to install a wood stove (such as a wood burning insert) into a prefab fireplace. Use caution when attempting to install after-market glass doors.  They may interfere with the fireplace’s design to circulate and disperse heat properly. Never attempt a renovation project – such as re-facing the wall around your fireplace – that covers louvers or air channels. Prefab fireplaces are AIR COOLED systems that require circulating cool air to help maintain safe operation.


*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 chimney cap). The flashing surrounding the chimney pipe easily becomes deteriorated over the years, contributing to water damage from rain leaks that lead to rotting wood. Deteriorated flashing can also allow birds and animals to enter the chimney chase (the framed “wooden” chimney area) where critters tend to build their 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.  Come back to Blue Sky Chimney Sweeps Blog area later this month for our next article:  Replacement Options for Prefabs

Have a Pro Install Your Wood Stove Insert

As winter approaches, thoughts turn to a warm fire and, naturally, to thoughts of how to help the open fireplace produce more heat while using less wood. Provided you have a MASONRY FIREPLACE, this can easily be achieved by installing a wood stove insert or wood burning hearth stove. The fireplace flue provides the venting – saving the cost of building a new chimney – but will require a chimney liner that meets the need of the new wood burning model.

close up of wood stove insertWOOD INSERTS are models made to insert into the fireplace opening. Provided your fireplace is large enough to accommodate it, this installation will provide a cleaner look and likely require the least alterations to the hearth or mantel as part of the project. The fireplace flue (properly modified as described later in this article) is used to vent the wood insert.

HEARTH STOVES are freestanding models that fit onto the hearth in front of the fireplace opening – or just partially inside of it – while venting into the (properly modified) fireplace chimney.wood stove insert in brick wall

Installing a Wood Burning Insert or Hearth Stove Will Normally Require the Chimney to be Relined as Part of the Project

Simply stated, the venting system is of paramount importance to how a wood burning appliance operates. The required vent size on a wood burning stove will be specified by the manufacturer, but most new stoves today use a 6″ round vent.

Just sliding a wood stove insert into a fireplace results in the stove having poor draft (hard to light and hard to keep burning), resulting in a dirty burning fire that creates excessive creosote because that big chimney contains a lot of cold air that makes it difficult for smoke to rise through. This installation would not be allowed. CREOSOTE is simply wood smoke that has cooled down and becomes solid and creates a fire hazard that requires sweeping the chimney. Left unchecked, a chimney fire can cause chimney explosions and dangerous house fires. Today’s new wood stoves, when properly installed using good venting practices, are designed for optimum safety, providing long burn times while producing less smoke, yet they simply cannot provide good results when they’re not installed following exact venting requirements of the stove manufacturer and fire safety codes.

A standard fireplace – also considered a wood burning appliance – that has an opening of 36″ wide x 30″ tall needs a much larger chimney area than a wood stove with an opening of perhaps 20″ wide x 15″ tall. 

The AREA of the chimney should be 1/10th the size of the opening for a square or rectangle flue (though severe rectangles should be larger), or 1/12th the size of the opening for a round chimney flue.

As an example, our open fireplace example is 36″ x 30″ = 1080 sq. inches, and the chimney would need to be at least 10″ x 11″. Most commonly we find this fireplace will have a flue tile measuring or 12″ x 12″ (interior dimension roughly 11 x 11), a standard size that’s readily available at the brick yard. 

11″ x 11″ = 121 Square Inches
The area of a 6″ circle (the size of the vent on the wood stove) is 28.26″

This means the 12″ x 12″ chimney tile liner is MORE THAN 4 TIMES THE SIZE REQUIRED BY THE WOOD STOVE, therefore relining the flue to down size it is required.

Today’s new wood stoves are pretty finicky burners. Catalytic converters and other clean burning technologies demand strict adherence to venting requirements. The venting, along with close adherence to combustible clearances, really is a job best handled by a pro.


diagram of chimneyThe best alternative for lining your fireplace chimney to accommodate a wood stove is a stainless steel chimney liner. Stainless steel is designed to withstand higher temperatures than those experienced in a chimney fire, providing an extra layer of safety. The stainless steel liner extends all the way from the flue outlet on the wood stove to the top of the chimney, providing a seamless passageway for smoke to rise and exit quickly to the atmosphere. High-tech wood stoves, installed with the appropriate size liner, will burn the wood more completely, efficiently extracting the available btu’s in the wood and transferring that heat into your home. You’ll enjoy using much less wood; a wood stove will hold about 1/4 as much or less wood than the open fireplace, yet burn for 6 to 10 hours or more. Combustion technology reduces smoke output for cleaner air.  Used regularly, you may enjoy heating cost savings of many hundreds of dollars each winter. 

Please call BLUE SKY CHIMNEY SWEEPS to discuss and plan your new wood stove installation.