Chimney and Flue

The word Chimney and Flue are just about the same thing, except a chimney can have several flues in it. Don't let the two words confuse you; often times the words are used interchangeably.

If you have a wood fireplace, you cant vent your fossil fueled heating appliance into the same flue. If you only have one flue and there's a fireplace on it, you need to build another chimney (or better yet, install a sealed combustion appliance).

Chimneys are often mason such as brick, or cement chimney blocks with brick around it for esthetics. In the mid-20th century chimney installers started installing clay liners in the flues, which were more resistant to condensation damage. Actually, back in the mid-last-century there weren't many heating appliance that ran at low flue gas temperatures, but they must have known something would change, because when the 1970s came around boilers got smaller and the flue gas temperature became more of a concern.

Chimneys can also be made of metal. There are generally two styles. Gas fired appliances would vent into what's referred to as B-Vent. Its a somewhat inexpensive double-wall galvanized pipe. The other style is also known as all fuel, you may even here the term triple wall, or Metalbestos, which is actually a name brand. So, simply put, a gas appliance can vent into either a B-vent or an all-fuel chimney, but an oil appliance must vent into an all-fuel chimney.

Many building codes are changing and it is becoming increasingly difficult to connect new gas fired appliances into the same existing chimney. This is another reason to consider sealed combustion appliances, because they're safer and they're also more energy efficient.