Overall I am very happy with the energy efficiency of my new house. I spent a lot of time in both the planning and installation of the air seal and insulation components of the home. I used blown fiberglass in 2×6 walls, and close to an R-60 level of blown fiberglass attic insulation. I also chose to use higher efficiency heating and cooling components, most notably a 96% efficient variable speed dual fuel furnace. However in the summer our total utility bills (elec + approx propane) were around $140. While in the winter the totals have been closer to $250 dollars. Propane consumption being the differing factor. The house is well shaded, which is a factor that I am sure helps. What I am wondering is whether this difference between seasons related to the fact that fiberglass insulation (especially in a vented attic?) due to convection loses effectiveness in cold temperatures compared to warm. I am tempted to blow in 3-4 inches of cellulose on top of the fiberglass which I have read may help to stop the convection somewhat since air does not move as freely through the cellulose. I am just slightly concerned about the fire rating of cellulose. Is that fear unfounded? Is there a better solution? The house is about 8000 conditioned square feet and neighbors who had their homes built by production or semi-custom builders have utility bills 2-4 times what we pay, so I really don’t know how much more room for improvement there is. But if there is something that can be done, especially in a DIY capacity I’d like to do it. Thanks