DIY Network

The Anatomy of a Fireplace: Flues, Chimneys and More (page 1 of 2)

Learn about the various parts that make up a fireplace and when they need to be repaired or replaced.

Excerpted from Do It Yourself Home Improvement

More in Home Improvement

There are several things you need to consider when choosing a new fire or refurbishing an old one. You may need to install a new flue, or have an existing chimney lined or relined — the main types of flue are shown here. If your current flue does not need renovating or replacing, it will be easier to choose a fire suitable for it. Unless you have a direct vent fireplace or balanced flue, you need to consider ventilation; fires require an air supply to burn well. A lack of wall space can make it desirable to cover up a fireplace, either leaving the recess or making it flush with the wall.

Gas Safety
Vent-free fireplaces have an oxygen detection safety-pilot (ODS) that automatically shuts off the gas supply if the oxygen level in the room falls to 18 percent. In 1995, the Vent-Free Gas Products Alliance of the Gas Appliance Manufacturers Association did a study on indoor air quality as it relates to domestic vent-free gas heating products and determined that vent-free gas heating products meet or exceed the most current and nationally recognized standards and guidelines for indoor air quality. Install a carbon monoxide detector whenever operating any gas product in the home.


As fires burn, they give out combustion gases, which are carried out of the home by a flue. The main types of flues are discussed below. As the gases are carried out of the house, they must be replaced by fresh air. In older houses, natural drafts were relied upon to provide this constant airflow. In modern, well-insulated homes, it is unlikely that a natural airflow exists, so ventilation must be provided. Some flues (balanced flues) have a built-in air intake. Ventilation requirements should be specified for particular fires. Fires and flues need to be checked annually by a professional to ensure that they are working safely and efficiently, according to the National Fire Protection Agency.

Fireplaces Without Chimneys
There are several types of flues that do not need a chimney. Two common designs are shown below and flueless fires are also available. The type of flue you need will normally be specified by the fire manufacturer. Some fires only radiate heat, but the fires shown here also warm air from the room by circulating it inside of the body of the fireplace, separately from the combustion process.

Balanced Flue
This kind of flue is built into the fire and runs straight through the wall behind. It takes fresh air in and lets combustion gases out. A balanced flue is used with glass-fronted fires so there is no contact between the fire and the air in the room.

Courtesy of © 2007 Dorling Kindersley Limited

The combustion gases are cleaned by a catalytic converter and released into the room, making flueless fires efficient because no heat is lost via the flue. Flueless fires can only be installed in larger rooms. The minimum room size varies, so carefully check the manufacturer's specifications.

Courtesy of © 2007 Dorling Kindersley Limited

Power Direct Flue
This type of flue has a fan to suck combustion gases through the flue and expel them outside. Power flues can be extended, so it may be possible to install a fireplace away from an external wall. An electric supply is required for the fan.

Courtesy of © 2007 Dorling Kindersley Limited

« Previous12Next »

Excerpted from Do It Yourself Home Improvement

© Dorling Kindersley Limited 2009