I think the oak tube goes inside the stove, this is hindsight.
The 5' of 2" tube will be less restriction than my 13' of 3".
Does the p61a have a cover with a perforated knockout/cutout in the back cover? That is intended for a 2" tube, cutting it for a 3" and making it look respectable is a pain.
I used 3" galvanized vent pipe, same tubing as hvac duct, 3" because i went about 13' with a few 90's and wanted it to flow well. Also, thru the wall i used 4" with a screen built in and a rain cover, the screen mesh is about 3/8", low restriction but won't keep the insects out. The big box store have it, my came from menards, about $110.
The outside of the stove oak intake is 2-3/4", i wrapped a 3/4" wide by 3/32" thick aluminum strip around the oak tube on the stove to take up the difference between the 3"id tube and gave it a good coat of silicon to seal and glue it together. That was second attempt, first attempt was a 1/8" filler strip, 3" - 2-3/4" = 1/4"/2 = 1/8", simple, wrong, the tubing isn't very round, the piece i made wasn't very round and the oak intake isn't very round, just didn't fit. The 3/32" fit well.
