I said over 600. I'm talking 625 or 650°F. The WS info that came with the stove says overfiring is at 675°. I'm not sure if you are referring to a "generic" overfire of a stove or the PH in particular. If this 700lb soapstone stove is getting that hot (675°F) something is surely to start to degrade. I see the internal parts glowing (such as near interior firebox exit) quite often even in the 500-600°F range and with the air almost completely turned down.
I'm not sure why almost every post I write needs to be refuted or discredited. That's not very inviting to provide updates to everyone. Some may understand why I'm looking for help elsewhere.
The window is open a couple feet from the stove so a house measurement is not going to help there. Perhaps something to measure pressure at the chimney level outside near the chimney cap... but the pressure at the stove room is fully neutralized.
Two years ago when the Chimney installer came they did take a few parts of the pipe apart and did not think anything was wrong. This is the NYSCSG/CSIA/NFI/NFPA/F.I.R.E. certified installer and Certified Master Chimney Technician that says my chimney is 100% built properly. They were the most "decorated", experienced and heavily reviewed Chimney Installer/Chimney Sweep available.
If I leave the door open it seems to be making the smoke much worse. So after a reload I leave the air open all the way for ~10minutes until the fire has spread nicely, then I turn down to halfway until the temperature reaches about 400°F, close the bypass, then slowly start to lower the air intake to ~10% open as the stove warms passes 450°F. Usually it's about 500° before I get to the final 10% open. If I turn down much slower than that there is a higher chance for slight smoke leakage during the burn.
Some stoves and or wood in situations cannot go under 40/50 percent without smoke. Try a smaller load if you are worried about over fire but try running stove at 50 percent air inlet or tad under for a while. I bet when you turn your stove down to 10 percent you are getting smoke out the chimney (or eventually during the burn) and it is blowing allover you house area outside.
"its right after we close the door there's some smoke spillage around the stove".
On reload when I say leave door open cracked 1/2 inch for a minute or 2 min then close the door. But add some kindling with each reload.
If you want to lower draft get a key damper., but id wait until you take the pipes apart to clean.
" but the pressure at the stove room is fully neutralized" How do you know this without equipment or smoke pencil? Plus it can change during the burn cycle and temp of room and chimney.
The stove pipes need to be cleaned and taken apart each year and stove inside swept and vac. , especially if you had a creosote smell with a previous stove.
My stove is in the basement and it took a long time, $$$ and lots of headaches to solve the smoke issues. Many people on this forum gave me great advice or advice to try something different.
But you need to start with small logs and 2 or 3 year wood, not oak. Every stove problem needs to start with the first rule...rule out any wood problem whatsoever.
Then try burning differently. Not 10 percent air. Shut off all fan/filters.
Try a wind cap. What cap do you have?
Then next step maybe the oak.
"If you open the door and get a burst of air how do you guarantee none of the air and fumes in the intake channels stays 100% inside the stove? " A smoke pencil test near the door will tell this. Also, watching the rear of stove, with a mirror, camera video or flashlight on reloads. Even with a good draft on a Magnahelic gauge you can get smoke out a secondary air inlet. I have proven and tested this on my stove.
Please keep us posted.