You asked whether newer, high efficiency furnaces operate at substantially higher temperatures than older furnaces, and if so whether they necessitate changes in the venting system in the homes in which they are installed.

High efficiency furnaces actually operate at lower exhaust temperatures than older furnaces, according to Joel Gordes, a consultant with the Energy Conservation Management Board. (The board reviews the conservation programs developed by the electric and gas companies. ) As a result, they do not necessitate changes in the venting system in the homes where they are installed. In fact, because of the lower temperature, they can use plastic piping in the venting system, whereas older furnaces must use metal piping.

KM: ts