Outlet and switch plate seals are readily available at hardware stores and online. Mine came with a bonus pack of plastic outlet plugs.
Air infiltration is one of the worst culprits of heat loss and energy consumption. Have you ever put your hand by an outlet on an exterior wall? If it wasn't well insulated it was probably blowing in a significant amount of cold air and leaking out all your warm air! Well, insulating outlets and switch plates is just about one of the easiest and relatively cheap things you can do to eliminate heat loss without having to re-insulate your entire home.
What You Need
Outlet and Switch Plate Seals (can be found at any hardware store or online)
Low V.O.C. Caulk (optional) &mdash we recommend OSI Insulating/Energy Sealing Caulk
1. Turn off power to area your are working on.
2. Remove the cover plate from your switch or outlet box with a screwdriver.
3. Select the proper foam seal and remove the cut outs. If you are sealing a multi-switch box, use the appropriately sized foam seal, or trim and duct tape together multiple seals for the correct length.
4. Place the seal over the open face of the wire box and line up the holes.
5. Replace the switch plate or outlet cover.
6. Bonus points for using those outlet safety plugs to further eliminate heat loss through outlets.
Additional Notes: To take the insulating one step further, we'd also recommend caulking the perimeter of the outlet boxes to the surrounding drywall, this will also help eliminate drafts and sound transfer.
(Images: Rachel Wray)