Flue gas is a type of exhaust gas that exits the atmosphere through a pipe often called a flue. Flue gas can be seen exiting power plants, a fireplace, oven, boiler or steam generator.

A flue gas Desulphurisation (FGD) plant removes Sulphur Dioxide from the flue gas before it is released into the atmosphere and hence reduces our impact on the environment.

Usually refers to a gas fireplace, since wood fireplaces are vented by the flue (chimney) Gas fireplaces can be vented (flue) or unvented (no flue)

Of course If the flue is sized properly

A flue gas analyzer is used to check the chemicals in the gasses in one's flue. They can be purchased at most home improvement stores or stores that have a home improvement section.