Chimney Terminology:
Chimney or Flue or Vent?

Chimney terminology can be confusing.

Whether you’re doing online research or talking to a chimney and vent professional, a sound understanding of associated terminology can help you ensure your chimneys and vents provide optimal protection for your home. This guide will help you understand chimneys, vents, connectors and flues.

A chimney is a passage to carry the products of combustion outdoors. Chimneys are made to be able to vent all types of fuel: gas, oil, and solid. Chimneys may pass through the house (including the living space), be outside of the house in a chase (a surrounding to protect the chimney against weather), or be outdoors. Chimneys may be masonry or factory built. Factory built chimneys are generally stainless steel, and may be covered by a chase (for protection or decoration), or left as is.

While chimneys vent fuel, they are not considered “vents”.

Understanding Vents

Vents are used to carry the product of combustion for lower temperature appliances (those using gas or oil) outdoors. Vents may pass through the house, or run outside of the house, so long as they are protected from the elements. Vents need a degree of temperature protection, otherwise their low temperature combustion products may be too cool to properly vent. This could cause a dangerous amount of flammable byproducts to collect in your vent.

The top of a vent must be exposed to the outside to allow the byproducts to be released, but such exposure will not cause problems given the rest of the vent is properly set up and protected. Sometimes a vent fan is installed to help push (or pull) low temperature byproducts from the vent.

Vents are always factory built. They are not chimneys, as they cannot handle the high temperature of wood combustion. Some vents, however, may run through a chimney, given that anything else venting through the chimney is contained in a separate flue.

Understanding Connectors

Connectors are also known as “stovepipes” or “smokepipes”. They pass from an appliance to a vent or chimney. There are a variety of connectors available, and the type of connector needed depends on the type of fuel that needs to be vented.

Understanding Flues

A flue is simply a passage for conveying exhaust gases from an appliance to the outdoors. A flue may be a duct, pipe, vent, or chimney. An unlined chimney is technically a flue, even though an unlined chimney is a fire hazard. This can cause confusion, as many view flues not just as a passage for venting, but as a safe passage for venting.

Understanding Chimney Liners

There’s a misconception that masonry chimneys are simply made of brick. This isn’t true. The uneven and porous surface of brick provides a space for combustion byproducts to accumulate. This is a major fire hazard. Rather, chimneys are lined, so the smoke passes over a smooth surface that helps prevent excessive accumulation of combustion byproducts and minimizes the chance of fire. Chimney liners are also called “chimney flue liners”. The terms are largely used interchangeably.

Traditionally, chimneys were lined by fireclay flue tile. This special tile is carefully laid inside chimneys to provide no ridges or spots for accumulation; the tile is finished to a smooth, nonporous surface. This classic chimney liner can be difficult to fix should tiles become damaged deep inside the chimney.

The most popular modern liner is stainless steel. These liners can be inserted in unlined or tile lined chimneys. They are inexpensive compared to tile liner, easy to install, and easy to replace should any damage occur.

With a proper understanding of the differences between chimneys, vents, connectors, flue and chimney liners, you can have a better understanding of your chimneys and vents, and can more easily discuss any problems that arise and how to fix them.