Fireplaces, Heating Stoves, Flues and Chimneys - Please Help!!

I am based in Western Canada and I have a Vermont Casting NG fireplace. I have two holes on the bottom of the fireplace, one where the gas line comes in and another has nothing and these holes are by the main valve and fan. The floor right at the base of the fireplace(hardwood floor) is very cold and I can feel a draft entering the house. Just wait till the temp. reach -40 C around here. Since there is nothing behind the fireplace buildout, can I stuff a bit of insulation into the holes to reduce the draft or is that defeating the purpose of the fireplace as this is the location where fresh air is used for combustion?:confused:

Fresh air for combustion should arrive via the flue pipe's outer layer. Although you may have more air infiltration places, stuffing insulation in the hole, without the paper could stop it at that point. I would attack it from underneath the house, however, and use red electrician's gap sealant in a tube. It won't fall out, be pulled out by mice or be affected by moisture.