Hearth Products Glossary
Several words have one meaning in common usage and another meaning altogether in the hearth industry’s technical lingo. On this page, we have provided an explanation of commonly misunderstood words in order to avoid confusion in our communications. Some of our definitions are taken from the National Fire Protection Association standard book for Solid fuel appliances and chimneys, otherwise known as NFPA-211.
First, a hearth appliance is a device for containing a fire safely for heating or aesthetic reasons. For example, a stove is one kind of heating appliance intended for installation in the space being heated. A stove is not to be confused with a range, which is a cooking appliance typically found in the kitchen. Stoves are often categorized according to what type of fuel they burn: wood stoves burn wood, gas stoves burn either natural gas or propane, pellet stoves burn pellets, etc.
Another example of a hearth appliance is a fireplace. Open (non air-tight) fireplaces are mostly for aesthetic use, as their heat output is usually very low (sometimes negative efficiency). One difference between a fireplace and a stove is that stoves are designed to be used primarily with the doors of the appliance closed, so that you can control the flow of combustion air, whereas a fireplace, if it has doors, should typically be used with the doors open. The exception to an open fireplace is a high efficiency fireplace. This category has become a lot more popular over the last 10 to 15 years. Quite a number of this type of fireplace are available on the market now. They are very much like a wood stove intended for heat, but are designed to be built into a wall and heat with high efficiency.
Stoves are usually freestanding, i.e. placed away from any wall, to avoid setting the wall on fire. But there are stoves that are made to be installed into a wood-burning fireplace, and these are called inserts. People often decide to put an insert into their fireplace when they find out that their fireplace by itself is a poor heater. Quite frequently, we hear people refer to a prefabricated fireplace (below) as an “insert”.
Fireplaces can be either factory-built or masonry. Factory-built fireplaces are also called prefabricated fireplaces or zero-clearance fireplaces. It is not always easy to tell the difference, but factory-built fireplaces are made of metal and use a metal chimney. They are usually on top of a wood floor and enclosed by wood framing. Masonry fireplaces are made entirely from masonry material such as bricks or stone. They usually are supported on special supports called footings consisting of concrete poured on undisturbed soil.
Hearth appliances produce flue gases, which are the products of combustion plus some excess air. Flue gases are commonly referred to as smoke, but in technical lingo, flue gas is only smoke if it has a lot of visible particulates. An efficient woodstove will produce flue gases with the only visible component being steam, which is the water vapor produced from complete combustion. An efficient stove burns so cleanly that all of those dirty particulates that made the smoke black are burned up inside the appliance.
The flue is the passage the flue gases follow to get outside and into the atmosphere. For a wood stove, this is usually comprised of stove connector pipe (stovepipe) which runs from the stove to the wall or ceiling, where it connects into a chimney, which is thicker, heavier, and better insulated than stove connector pipe. Like fireplaces, chimneys can be either prefabricated or masonry. To be safe, masonry chimneys should contain some kind of liner on the inside to contain the flue gases. Usually, masonry chimneys are built with flue tiles, hollow tubes made of fireclay, as the liner. Metal liners and poured-in-place liners are also available, and comprise a more durable, better insulated flue liner than a clay flue tile.
The flue of a gas appliance is usually referred to simply as vent. The type of venting depends on the way the stove or fireplace is designed and manufactured. B-vent is a type of vent that has only one passage to exhaust the flue gases. Direct vent is another type of venting, which conveys flue gas to the outside as well as bringing outside combustion air to the fire chamber. Direct vent appliances are usually much more efficient that b-vent appliances and they comprise the majority of the gas stoves on the market today.
A pellet stove is a stove that burns wood sawdust that has been squeezed and pressed into small wood pellets under pressure. The pellets are usually ¼” in diameter and about 1″ long. No glue or wax is added to the sawdust; the pressure of the wood sawdust being extruded into a pellet causes heat and the natural lignin in the wood holds the pellet together.
Should you have any questions regarding something else you would like to understand about the terminology that we use, contact us. We welcome comments and questions regarding the definitions given on this page.