It was perfectly still outside with no wind. As you opened the door more, the neutral pressure plane dropped down some more. You were the only one who responded to my post and I thank you. If you don't mind I'd like to run by you the test results. 2nd floor has 7 recessed lights that are leaking into attic.
Flow is good when basement window open.
Basement flue is blocked off, but when opened cold air rushes in. Home is 5 yrs old with tight construction. Which could turn into stack effect once upper leaks are sealed. I also plan to chamber tech the smoke chambers to solve the breech and see if it worked, if not then I recommend reline. 230-3060 John Gulland describes this test in his seminars as well.