Here's a post for all those seeking validation for having delayed deep cleaning of the house, thereby increasing home biodiversity and allowing some unexpected species to join your Domestic Energy Reduction Team.
Websites like EnergyStar and ThisOldHouse tell you that houses lose a lot of energy through leaks in the top floor ceiling. Light fixtures, ceiling fans, attic fan louvres, smoke detectors that run off house current rather than batteries--all can provide small openings for your heated air to escape into the attic. I've tried using incense to find these leaks (the smoke would supposedly show where the air is escaping), but the smoke is hard to see. An unexpected ally in a less than perfectly cleaned home turns out to be spiders. They seem only to build webs where there's airflow. Ceiling fixtures that are tight don't have them; ceiling fixtures that are leaking air into the attic do. Once you find the leaks, you can follow the directions on the websites to plug them up. Same goes for windows in the basement.