I'm really not sure, it came with the new furnace... Canadian Tire has them for sure, though, so you might want to check them out, too.

Any house older than the 70s (and even then) is sure to have some leakage through the walls via the outlets. Our house is about 75 years old, with thin (frame) walls, so any little bit helps. :) There are tips available through the provincial gov't's website (Ministry of Energy, I think) on how to check for leaks in all kinds of places you'd never dream of, actually -- worth a look.