Prefab fireplaces are slang for ”factory built fireplaces.”
The single most important thing about prefab fireplaces (and fireplaces in general) is that they must be installed correctly and that they are inspected annually and cleaned when necessary.
There are 2 3 common types os wood burning prefabs. One is a radiant fireplace and the other is a convection fireplace. Radiant firplaces are not design to circulate air around the fireplace and out into the room, but to simply radiate the heat straight out of the opening.
The second type, convection fireplaces, do circulate air out into the room. For this reason there will usually be visible louvers above and below the fireplace opening. These openings must never be covered or have the air circulation blocked. This is part of the design that insulates the unit, preventing a fire hazard. A fan is often installed with convection fireplaces to help circulate warm air out into the room. If there is a fan control switch, the fan does not have to be turned on. Unfortunately most people report very little heat distribution form the use fo these fans.
The third type of Prefab Fireplace I call an EPA Fireplace or Hybrid Fireplace. These fireplaces are built much like wood stoves. They are heavy and have airtight doors like wood stoves and produce little soot and lots od heat. They emissions are regulated by the EPA (Environmental Protection Agency.) They are a great heat source, they are clean burning and use a renewable fuel source (wood.) Some have air ducting hook ups for heat distribution utilizing existing air ducts as a heat distribution system.
Down side of EPA Fireplaces- they are more expensive than other prefabs, they look more like woodstoves than other prefabs, they are heavy and more difficult to carry up and down steps and such (like wood stoves.) A tidbit of good news is that the chimney systems are often the same as other prefabs, making them light and relatively inexpensive.
The vast majority of prefab fireplaces, EPA Models excepted, consist of fireplaces made primarily of sheet metal. All of them, even the EPA fireplaces, usually have ventilation systems made of sheet metal. Many people refer to the ventilation pipes as triple walled chimneys. Though many of these chimneys do have multiple layers of sheet metal pipes to carry the smoke out of the house, they should not be considered as “regular” chimneys or class A chimneys which have multiple uses. Using these chimneys for other than venting the specific fireplaces they are designed to ventilate should only be done when an appliance is listed for use in this particular manner. If there is any doubt consult with a professional and/or local code officials in your governing jurisdiction.
There are many companies that do manufacture Class A or High Temperature Chimney Systems. True Class A chimneys generally are suitable for multiple uses. Many are listed for use with wood stoves, oil and gas furnaces. Though there are a few prefab fireplaces that are installed correctly with Class A chimneys attached to them, the majority of prefab fireplaces chimneys do not. The majority of prefab fireplaces have exhaust systems that are only designed to be used with a few fireplaces manufactured by that same company .
Refractory panels or fake brick panels that line the inner surfaces of prefab fireplaces can often be replaced. But, if your prefab fireplace is rusted out or warped from heavy use or otherwise badly deteriorated or has parts missing, it probably should be replaced. It’s age and size and whether or not the manufacturer is still in business or not will effect the likelihood of finding an exact replacement and/or reusing the exhaust (chimney.) More often than not, if the fireplace requires replacement, the entire system will need replacement.
Using prefab chimneys and fireplaces for venting wood, gas and pellet inserts and stoves and is sometimes possible. Their are several such appliances that are listed for use in this manner. But generally prefab chimneys cannot be used with other companies prefab fireplaces.
When replacing some or all of a given manufacture’s prefab chimney pipes, the manufacturer should be consulted to assure compatability of the new components.
A common repepair on a prefab chimney is replacing the chase cover or layer of sheet metal which covers the top of most exterior built prefab chimneys. Common to townhouses and some newer homes these chimneys are often protruding from the house and wrapped in siding. The top of the surrounding structure the chimney resides within is called a chase and the chase is covered with a sheet metal called the flashing or chase cover. Water often ponds on chase covers causing them to rust quickly. It is not uncommon for one to rust badly in 10 years or less. It is a good idea to replace them with a stainless steel cover rather than a galvanized steel cover.