Hi Anthony,
The following answers are based on the 2006 IRC - Fuel Gas Chapter 24, which would be the same in the 2006 IFGC.
Anthony wrote:I think I am correct that a double wall vent is class b, if it has a locking mechanism.
You have described a Type B Gas Vent, however, only those which are also listed and marked/labeled as Type B Gas Vent are Type B Gas Vents, i.e., one could have an unlisted/unmarked/unlabeled vent as you described and it would not be a Type B Gas Vent.
What is the minimum clearance to combustibles? I think I read 1inch in the mechanical code book.
Someone told me it was 2 inches.
The minimum clearance will be as listed by the manufacturer, but for a Type B Gas Vent the standard clearance to combustible material AND INSULATION (most people forget that part) is 1 inch.
A gas furnace vent should rise 1/4" every 12"?
True - for the horizontal portion of the vent, see below for a definition of horizontal.
2-45° bends are allowed OR one 60°? or are they saying you can have 2 45's and a 60° bend?
They are saying that you can install 45-degree offsets (plural, meaning more than one) except that you could install one (limited to one offset) if you installed a 60-degree offset. The vent is required to extend "in a generally vertical direction". If an offset if more than 45-degrees that part is considered to be "a horizontal section" and not a vertical section. Additionally, the maximum total offset of a vent and vent connector serving an appliance with a draft hood is 75 percent of the total vertical height as measured from the draft hood to the discharge opening within the Type B Gas Vent Cap.
Let's say the vertical distance from the draft hood to the discharge within the Type B Gas Cent Cap is 8 feet, which would be quite possible for a single story house (the minimum total height required is 5 feet), that means the greatest total offset allowed would be 75 percent of 8 feet, or 6 feet maximum allowed offset.
Condensate drain fall 1/8" for every 12" or 1%?
True.