I have an aluminum Gas Flue from my Furnace to the outside cellar wall with a power vent. Where the Flue exits the wall there is alot of open space to the outside. What kind of insulation can I use there? Can I use regular Fiberglass insulation? I don't believe the flue gets all that hot.

 

I would suggest you use mineral wool it is a more suitable to that type of situation... Your not likely to find the product at a Home Depot type store.. But you can find it at insulation wholesale supply houses or possibly a drywall wholesale supply house...

3 manufacturors of the product are
Roxul - Owens Corning - USG

Good luck

Jim