Electrical outlets that appear to be almost flush with the wall actually extend into a hole in the wall and are held in place by an electrical box. Most houses have an air or vapor barrier that is designed to stop drafts through the walls, but most electrical outlets make large holes through this barrier. You have several alternatives. You could seal off the old boxes and run the wiring forward to surface-mounted boxes, thus eliminating the need for the holes. Foam gaskets under the face plate would also help. For a neater solution, you can install polyethylene envelopes around the electrical boxes before nailing them to the studs. This "polypan" — used in new construction or major renovations — is then sealed to the vapor barrier. New construction also uses airtight electrical boxes. The 100 percent seal is made with airtight rubber box inserts that slide into the existing box.