We have been listing the things you should do to prepare your home for winter, in order of bang for your buck, as determined by the Rocky Mountain Institute (RMI), which figured out the cost in dollars per ton of carbon saved for each investment you make in time and money. See earlier posts here.

If you live in the north in a drafty old house, this is an important one. The window salesman may tell you that you have to replace those old wood windows, but they are often part of the character and charm of the house, the replacements are usually vinyl, and it costs a lot of money.

RMI suggests that weatherizing your old windows will save 621 pounds of carbon at a cost per ton saved of $25.02; I suspect it is much more money saved than that. These instructions are for double-hung windows, but they work for most kinds. The products I use are a seal and peel caulk (wonderful stuff; no matter how bad you are at caulking it just peels off in the spring) and heat-shrinking film. I lust after magnetic interior storms but that is more expensive.

1. Wipe the sill and the frame: Dust and dirt affect the ability of the tape to stick.

2. Caulk the windows with seal-and-strip caulk: I caulk every window in the house except our bedroom and doors to the balcony or spaces that we don't use in the winter. The gap between the window and frame can be large; just fill it up, it will all come off. The more consistent you are in applying the caulk, the easier it will be to remove-a small pleasure is when an entire window gets peeled in one continuous pull.

3. Apply the window film: A four-step process: (a) Apply the foam two-sided tape around the window; (b) Stretch the window film across, trying to keep it relatively flat and even; (c) Use a hair dryer to shrink the plastic; it goes completely flat and you won't even know it's there-although our cat found one window and left it in tatters. (d) Trim the excess.

Results: Fewer drafts, more even temperatures, lower heating bills and less fuel burned.

Difficulty level: Moderate