WBI,
My wife looked at the ducting that runs to the fireplace in the basement under the main floor subfloor. It appears that the fireplace installer may have erroneously swapped the connections where two ducts that connect to the fireplace . It appears that the duct that runs from the outside of the house that is supposed to supply combustion air may be connected to the cutout used for recirculating heated air through the house. I looks like the duct that runs from the office/dining room for recirculating heated air may be hooked to the combustion air cutout in the fireplace. The flexible ducts run up through the floor and inside of the sheetrook beside the fireplace so we can't see exactly where each of the two ducts connects to the side of the fireplace. However, it appears they might be swapped.
The flexible duct that runs parallel to the white PVC drain pipe is the combustion air duct. Just to the right of the combustion air duct, you can see the recirculating air duct that runs to the office. Based on the pictures in the installation manual, we think these two ducts run up through the floor into the wrong holes. Thus, the combustion air is trying to come through the long duct running to the office. That duct is probably too long to supply the combustion air. The longer duct can feed recirculating air because the recirculating air is forced using fans.
The fireplace company is sending out a technician to our house Wednesday of next week. We're a little disappointed they are taking a week to get out here but they said they are really busy this time of year.
Obed