Wood stove backdrafts
I just built a house of about 1500 s.f. It is double stud framing w/ spray foam covering the outer studs, and spray foam around all lighting fixtures in the ceiling and at the rim. We have an HRV. I got a Vermont Castings high efficiency wood stove (model CDW27007) in the basement w/ a 4″ diameter fresh air vent. I have run the stove about 6 or 7 times since we moved in. Three of those times it has backdrafted. The first time was after about 10-20 minutes I was just sitting there enjoying the heat/flames w/ my 2 year old and all of a sudden, the fire goes out and smoke starts billowing out from all corners of the stove (also a strange dripping like water on the top of the door coming out of the air intake???!!! Condensation or something?). The second time, it was running for about 10 minutes when my wife turned on the bathroom fan (panasonic). Again, smoke billowing out. I had her shut off the fan and it returned to normal. Third time, the stove had been running for about 20-30 minutes. We were up reading books with my 2 year old and the smoke alarm started going off. I run downstairs and once again, the fire is out and smoke is billowing out mostly from the top, next to the air intake lever. I can feel air coming in the fresh air vent 1 foot away. After 30-60 seconds of this it just sort of stops and the fire picks up again.
It starts right up initially every time and seems to draft wonderfully. I checked out side and it didn’t seem very windy, so I don’t think it would be any sort of wind preventing the draft suddenly. It seems baffling to me. The place that sold me the stove, suggested it was off gassing from the new paint, or a cold chimney. These are both incorrect because the chimney goes up the center of the house and I could see/smell the paint offgassing and it was not the smoke billowing out of the stove.
Does anyone have any ideas on why this is happening and how I can fix it? I would like to use the stove because we have access to free firewood.