The following are excerpts from a report of an energy audit conducted by a certified energy auditor.

Findings:

We found a large leak behind the gas fireplace where the vent pipe passes through the metal wall of the assembly.  This can be caulked from outside when the siding is removed.  Use a high temperature caulk to seal the flue collar to the vent pipe.

Other leakage was found in the basement at the band joist and sill plate, at framing corners for the bay window and fireplace cantilevers, and at the band joist that separates the garage from the basement.  Areas over the basement windows also showed leakage.

We did find one stud cavity in the cathedral wall over the thermostat had a missing batt. I found a batt under the blown insulation that filled a portion of this area and installed it.  The garage ceiling has an R-19 fiberglass batt installed, but this batt is touching the drywall instead of touching the floor above.  This is an important detail since the room is heated from the ceiling and warm air will tend to rise to the cathedral ceiling and away from the cool floor.

Recommendations:

We recommend that you have the leak at the fireplace repaired and have insulation blown into the floor joist cavities over the garage to fill the joist space. This will reduce heat loss through the floor, and more importantly, insure that the insulation makes contact with the floor that you walk on.  Install caulk or expanding foam at band joist seams in the basement that showed leakage.  Finally, install volume dampers at 4 to 6 branch takeoffs and use these controls to adjust airflow.