by matt walker » Tue Sep 17, 2013 4:13 pm
Welcome Dato. I'll give you my opinion, but I'm not sure there's any one right answer here. Most builds I've been involved in have used found/recycled materials as much as possible. It's a heck of a lot easier to find galvanized ducting used for free or cheaply than it is to find black stove flue pipe. Since it's not exposed to high temps in the mass, it's generally accepted as okay to use galvanized in there. Even if buying new, around here the galvanized can be bought in thin gauges for much cheaper than the black, which is typically 24g or heavier in my experience.
If money were no object, I'd go with the black pipe just because I find it easier to work with and its heavier gauge is reassuring when packing mud and rocks all around it. But I wouldn't agonize too much over it, around here it can be difficult to find 8" black flue pipe anymore since all the new wood stoves are 6".
As for chimney, if you can afford double wall 8" for your chimney your system will run better with an insulated chimney than without, but how important that is depends a lot on your system and how much heat you are taking out of the exhaust gasses in the mass. For most folks single wall is acceptable since flue temps will never be very hot at the exhaust, although if it's outdoors in a cool climate single wall might work against the system by creating a 'cold plug.'