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Wood burning fireplace inserts were designed to produce more heat than a standard fireplace. It is important to remember however that solid fuel inserts rely upon the original fireplace system meeting proper construction requirements as a masonry fireplace. So… you may be thinking – what does that mean?

Well, it depends… In the photos above all three show inserts installed into factory-built fireplaces. Two of them are ‘faced’ with stone but they are not actually masonry fireplaces. If you walk outside and look up the pipes and terminations look like those shown below. Any time a chimney pipe or a sided chase are visible outside chances are you have a factory-built fireplace instead of a masonry fireplace, even if you see stone or brick inside your house. Factory built fireplaces are not subject to testing with solid-fuel inserts installed.

Before considering the installation of a wood burning insert into any fireplace a full Level II inspection is required according to the NFPA211, the industry standard on Chimneys, Fireplace, and Venting Systems for Heat Producing Appliances. The reason for this is simple. There are many factors to consider whenever you bring fire into your home. Fire is always dangerous and whenever harnessed to bring into the home consumers and installers must do their due diligence to make sure the fireplace the insert will go into is suitable for that purpose and won’t create a fire hazard down the line.

Tested Clearances Are Invalidated

Every prefabricated fireplace has standards and clearances that must be met to ensure the safety of the homeowner. The addition of a fireplace insert with drastically different heating characteristics can alter these clearances and potentially change the heat signature of the entire appliance and venting system. In these cases, the appliance will overheat and any surrounding woodwork or flammable materials could ignite.

Many wonder if we could add an insert, then perform new tests to ensure everything is okay. Unfortunately, this isn’t an option either. There are currently no standards from the Underwriters Laboratory (UL) for testing this type of set-up though beginning at the end of 2021 discussions began at the request of a fire investigator from Ohio who has seen hundreds of fires related to inserts in factory built fireplaces over the past several decades. Currently a standard is in development (UL 1391) but there are still many issues the standard cannot address with testing as they are trying to put new retrofit appliances/inserts into systems that have already been tested. Factory-built fireplaces and chimney systems are only designed to use the parts they were tested with as any other parts or components can alter the heat signature of the system and invalidate any tests performed – essentially making the whole system an untested gamble with the lives of those in the building.

There is often confusion surrounding the codes, standards, listings (tests), and manufacturer instructions as they relate to these types of installations as insert manufacturers often say in their manuals that their inserts are ‘approved’ or ‘listed’ for installation into factory built fireplaces. The truth is there is no standardized testing for these types of installations and manufacturers are silent on exactly what type of testing has or has not occurred internally. The truth is that insert manufacturers are willing to gamble with your lives and take the risk as they don’t feel enough losses occur to stop the practice of recommending these types of installations.

For more information on the specific codes, standards and potential issues if you are considering this type of an installation please read this document that our owner put together for the task group formed by Underwriters Laboratory (UL) to explore this specific issue.

Download: Current Issues with Solid-Fuel Inserts in Factory Built Fireplaces and Chimneys

In the end, most prefabricated or factory-built fireplaces don’t allow inserts to be installed into their systems. Some specifically preclude the option. And many older models won’t even have language regarding inserts in their manuals at all. Remember, you are putting fire into your home and may be taking a little used factory-built fireplace and trying to turn it into a constantly used heating appliance with the installation of a wood insert… are you willing to gamble with the safety and well-being of your family and home? 

The two photos above show inside a chase behind a fireplace with an insert installed. Both studs change color and darken dramatically, especially on the right side where the framing is immediately behind the fireplace body. This indicates that the heat signature of the appliance has been altered and over time may overheat and ignite these materials. Below are close up shots showing these areas. 

Fireplaces & Inserts are Tested With Different Standards

Another important factor to keep in mind is just how these units are tested. UL tests prefabricated fireplaces and factory-built inserts separately, and each system must pass a wide range of tests to get approved. Factory-built fireplaces are tested to the UL127 standard which does not include any testing for inserts or anything approaching the weight of an insert. Free-standing wood stoves and wood inserts are only tested as freestanding room heaters only and are not inserted into any type of fireplace or enclosure. It is important to remember that just because a fireplace passed the UL 127 tests successfully it doesn’t mean testing would have been successful with the insert installed. In the end, assuming your insert will be fine just because your fireplace seems okay isn’t a viable option.

Essentially, because there is so much variety when testing both prefabricated fireplaces and factory-built inserts, it is hard to guarantee combining any two would produce good or safe results unless they were specifically tested together.

A Lot of Factors Simply Don’t Add Up

In the end, when it comes to installing an insert into a prefabricated system, there are many things that simply don’t add up with and that insert manufacturers aren’t able to provide clear answers for. A few examples of some common issues are outlined below.

For example, approving the addition of a 300-500 pound insert into a prefabricated unit that should only hold up maybe 100 pounds of wood doesn’t make sense. The math simply doesn’t add up and over time that additional weight can start to crush the sheet metal supports beneath the fireplace and overheat combustibles beneath the system. If supports are added will they transfer heat the combustibles beneath or obstruct the air flow required for the original fireplace to cool itself properly? We simply don’t know.

Along with this, some inserts that are “approved” for installation into factory-built fireplaces want high temp or HT tests be performed and passed by the chimney systems through which they run. Many of the factory-built fireplaces found in homes today were never tested to the HT standard, especially if they are older. For example, if the fireplace was manufactured before 1993, there wasn’t even an HT test available as part of the UL127 test for manufacturers to use. After 1993 the HT test was still optional. As such any insert manufacturer wanting a chimney system that was tested to the higher HT standard should not be installed or the system could overheat surrounding combustibles even if clearances were maintained. Liners are also not tested in chimney piping systems in either the liner tests (UL1777) or the piping tests (UL103 or UL127).

Another common issue is that the surrounds and faceplates used with inserts are often installed to block air cooled channels designed into the original fireplace. These channels are required for the fireplace to properly cool itself when in use and the fireplace manufacturer instructions will specify that these air inlets/outlets cannot be obstructed by any means. Altering or blocking them fully or partially can change the heat signature of the appliance behind the wall and invalidate tested clearances. In the end this can create a major fire hazard even though on the surface everything looks fine.

Below are a few pictures of fireplaces where the inserts blocked these air cooling channels in or out of the fireplace.

In the end, it is important to remember that there are no standardized testing criteria when it comes to installing an insert into a factory-built fireplace. There is currently no way to even formulate a test to approve this process though since 2021 UL has a committee working on a standard to try to address these and other issues at this time. Even if or when a new standard is released however it is important to remember just how many brands, variations, design types, and variables exist. Testing them all is impossible and making extrapolations with any testing performed gambles with the lives of the consumer.

When there are many viable options to replace these older fireplaces with new high-efficiency fireplaces designed to heat and tested to be enclosed in combustible construction how could we in good conscience consider any other option?

Our Policy

While other hearth dealers may install inserts into factory-built fireplaces, this is a service we have chosen NOT to offer. There are simply too many safety risks associated with combining two systems that don’t meet all of the requirements of the manufacturers involved, or for which testing data is not available. We feel that doing so would jeopardize the safety of our customers.

Here’s what we suggest – rather than install an insert into a factory-built fireplace, remove the prefabricated unit altogether, then install a high-efficiency wood or gas fireplace instead. Fireplace changeouts like this are becoming very common as the useful life of these factory-built fireplaces are exceeded. Factory-built fireplaces were only designed to last for 20-25 years and many of the fireplaces still in service exceed that timeframe, sometimes by decades. By replacing a factory-built fireplace instead of slapping an insert into it we can be sure that it meets and exceeds all tested minimum requirements and continue to put your safety and peace of mind first in all that we do.

What We Can Offer Instead

Like we’ve mentioned, removing your entire prefabricated unit is always the better option if you’re looking to upgrade and is often less intrusive than anticipated. When replacing a fireplace this often allows us to address other issues that may not be readily apparent: cold air down drafts, rotted wood in old chases, missing insulation, improper firestops, and fire blocking, or old outdated finishing materials used around your fireplace. Working with us you will end up with a system that is functional, efficient, and suitable for continued use day in and day out.

You don’t want to put lipstick on a pig with an old fireplace that is decades old behind the facade and questionable testing performed. In the end, if you want to work with professionals who care about your safety first and foremost in all they do – that’s where our team is qualified and excited to help! We install fireplaces, stoves, inserts (where suitable), and factory-built fireplaces, so we know the ins and outs of installation. Whether you are interested in wood, gas, pellet, or even the newer electric options, we can help.

When it comes to building a fire inside of your home, staying safe and installing products within the bounds of how they were tested should always be the number one priority. Don’t take any chances – rely on our experienced and educated crew to provide you with the high-quality level of care you deserve.

Call us at 970-234-3330 today to get started!

Last updated 2/20/2024