Roof Jacks & Extensions.
Nordyne/Miller/Intertherm Interior Roof Jack Extension (FM-901935)
This interior roof jack extension lengthens the roof jack connection to the furnace by 10". The extension is not adjustable, but the roof jack is. The inside pipe measures 5" in diameter and the outside pipe measure 8.25" in diameter. (These measurements were taken on the non-crimped end; the crimped ends will be slightly smaller.)Note: The entire interior extension must be exposed below the ceiling. Connections cannot be inside attics.