We are starting the construction of a Rumford fireplace, and trying to follow the specs as much as possible. One point that we do not feel comfortable with is the flue size. The only info we have found for sizing the flue says that the flue should be 10% of the fireplace opening. Our fireplace opening is large, @ 60" square. This 3600 sq. in. X 10% = 360 sq. in. Using a square flue, this would be 19", which seems like overkill. Also, in this discussion board, there is mention that by keeping the flue size down, the creosote, etc., stay in gas form, rather than cooling and condensing in the flue. Any advise on this would be greatly appreciated.
