Factory built, or prefabricated fireplaces, are relative newcomers to the fireplace scene, commonly available only for the last 30 years or so. Unlike traditional site-built masonry fireplaces, most factory built fireplaces are made of metal, and come from the factory as complete units with a firebox, a specific chimney system, and all miscellaneous parts. With proper installation and maintenance, they can give years of service, but there are some special considerations owners of these systems should be aware of:
1) The factory-built fireplace and chimney are a complete system, engineered to work safely and efficiently together. Both units(fireplace and chimney), undergo testing together, then are listed specifically for use with each other. To insure a safe system, you MUST use the exact chimney specified, along with the specified rain cap, flashing package, and all other system components.
2) Most factory built fireplaces are tested and listed as decorative heating appliances and will not withstand the abuse often heaped on their masonry counterparts. Although they are tested to U.L. standards, severe overfiring and chimney fires will often badly damage these units. Regular yearly maintenance, cleaning at generally 1/8″ buildup, and careful monitoring can assure a safe enjoyable system.
3) Many prefab chimneys, especially older units with an imitation brick housing above the roof, seem to be a preferred nesting site for birds in many areas. It is not unusual for chimney sweeps to take literally buckets of nesting material from these chimneys. This nesting can catch fire directly, or it can block critical air passageways between layers of metal chimney pipe, allowing the chimney to overheat. Both scenarios routinely cause house fires. Most after market chimney covers do not correctly address the problem, and can often make the situations worse. A careful screening of all potential nesting areas with the proper sized screening may be in order.
4) Finally, prefab fireplace systems eventually just plain wear out. Models go out of production and manufacturers go out of business. A factory-built unit will reach the end of is 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. Keep a close eye on an aging unit, and be prepared to send ole faithful to the great recycling plant in the sky before she fails completely.