Sounds like poor draft. This could be negative pressure, not untypical in a basement install. If this is the case another stove could have the same problem. What type of chimney does the stove connect to? What is the ID of this chimney? Also this could be an altitude issue. You need more chimney height at 6000 ft. How tall is it?
Ok, here are the chimney measurements. Distances are as specified, to the top of the pipe opening (not the top of the chimney cap). I do not see any marking on the pipe themselves, but I have manuals. But neither distinguish which is which, but both are the same type/grade. One or both are Security Chimney, ASHT High Temperature (to 2100 degrees), Type HT. On the interior, the Scan 61 pipe has "Made in Canada" stamped on it. Security Chimney is Canadian.
Upstairs (where Vermont Casting is) - 8" diameter pipe.
20' - 4" from floor grade, or 17' - 4" from stove vent. Straight up, no bends.
It is 3 or 4 foot over highest portion of roof top (on the side where the prevailing winds come from, thus far).
Downstairs (Scan 61) - 6" diameter pipe.
26' - 8" from floor grade, or 23' - 8" from rear stove vent. One 35 degree bend, about 20 inches length, about 20 inches after stove rear vent, then straight up.
It is 2' over the highest portion of roof top, on the opposite side of the prevailing winds (so the little high portion of roof is between it and the prevailing winds).
Some pics attached. Does the Scan's pipe look sufficient?