I cannot comment on your plan to have two stoves into one flue, I suspect it would be dangerous as carbon monoxide is heavier than oxygen and will sink if given the chance.
That being said running a smaller diameter flue will simply limit the stove to the max flow of the pipe. So imagine you have a 6" pipe with damper in the flue and you close the damper slightly. same effect so you will be limiting the total flow. your stove may or may not run a full power as a result.
I built my own wood stove from scratch it is sized for a 1200-1600 sq ft' house and my cabin is only 900 sq ft but drafty. I originally built it with a 6" flue but ran it for the first year on the existing 5" flue using an adapter that I made myself. I ran it until I decided to swap out the flueto 6" to see what would change. what changed was total heat output.
with the 5" flue it was very precise on adjustments, with the 6" flue total flow went up but it became harder to throttle down during the daytime when less heat was needed.
good luck.
That being said running a smaller diameter flue will simply limit the stove to the max flow of the pipe. So imagine you have a 6" pipe with damper in the flue and you close the damper slightly. same effect so you will be limiting the total flow. your stove may or may not run a full power as a result.
I built my own wood stove from scratch it is sized for a 1200-1600 sq ft' house and my cabin is only 900 sq ft but drafty. I originally built it with a 6" flue but ran it for the first year on the existing 5" flue using an adapter that I made myself. I ran it until I decided to swap out the flueto 6" to see what would change. what changed was total heat output.
with the 5" flue it was very precise on adjustments, with the 6" flue total flow went up but it became harder to throttle down during the daytime when less heat was needed.
good luck.
