[Daox]

You may think the house is well insulated, but you never really know unless you have an energy audit done. I highly recommend this. They cost a few hundred dollars, but they tell you exactly what needs to be done with the house to cut down on your heating bill. They also come back once you are done doing improvements and can qualify you for tax credits that can more than pay for the audit price. My guess is even if its well insulated, its probably not sealed all that great. This is the most common problems with houses.

Congrats on the house btw!