stakirk wrote:The stove is installed in the lower level of out raised-ranch house with the factory-specified 6" pipe through the masonry wall and then 12" triple-wall chimney outside.
The stack is 12" or you have 12' above your stove in chimney height? Either of these could be your problem. It has been very warm lately and that sours a draft. It is considerably colder tonight and if your problem is clearing up you need more draft. 60F is about the limit for a lot of hand fired appliances unless you have a nice tall chimney.
Once had trouble with a blocked chimney, it was a not very happy racoon.