I spent the afternoon putting plastic film on my windows. It was supposed to be a short project, and I do get better at it every year, but it still ended up taking about an hour per window.

I think it's time well spent. According to one article I read, it can cut your heating bills by 30 percent. That's some serious money.

The film comes in kits that you can buy at hardware or discount stores. The two brands I see most often are Frost King and 3M. I like 3M better--I think the tape holds better and comes off more easily at the end of the season, and I think the film is a little bit higher quality--but I buy the kits in the spring at a steep discount and store them until winter, so I don't really get to pick and choose much. And I don't think the 3M is superior enough to be worth paying full price to get.

I have 10 windows. Four are newer and more efficient, so I don't put film on those. Maybe I should. Five of the others have those awful aluminum frames from the 1960s, and many of them are single-pane. I'm going to replace those windows in a year or two, but in the meantime insulating them makes them leak heat considerably less, and it's cheap. Buying off season, it probably costs me $1 per window.

I have another trick to save money. I tried this out two years ago, when I didn't have a job and I didn't have any money. I ran out of film and I still had windows to do, but I had saved my scraps. So I taped some scraps together with clear packing tape (a big roll costs $1 at Dollar Tree) to make a piece that fit one of the remaining windows. It worked fine. It didn't look good, but at the time I was making $400 a week doing odd jobs so I didn't care about appearances.

This year I wasn't going to do that. I had so much film, I was going to have some left over to do one of the smaller windows next year. But the piece for my sliding glass door was considerably smaller than the box said, and of course by the time I realized it, I'd already cut the piece and ended up with something that covered approximately half the door. Worse yet, it was 8 pm and all the stores were closed, so going and buying a new kit, at full price, wasn't an option. My Scottish blood probably would have staged a revolt at that, but the option wasn't on the table.

I can justify it another way too, though. Oil is at $100 per barrel now. Do I need to consume more oil just to avoid having seams in my sliding glass door? I think I'll save some money and conserve a small amount of oil and live with the seams.

One way I found to reduce the seams is to mount the scraps on the window as tightly as possible, then put packing tape over the joint. I used to lay the pieces on the floor and tape them together before mounting, but I think taping the mounted pieces ends up looking better, and the process goes faster. Surprisingly, when I shrink the film with the hair dryer, it doesn't seem to have much negative effect on the cheap dollar-store packing tape I use.

Some people skip the kits altogether and just buy the tape (3M's tape is available separately), and either buy a roll of shrinkwrap film from a packing supply store or a big roll of food-grade film from Costco and use that. That may be an even cheaper option than buying the kits off-season, and it's certainly more convenient. I don't know what those rolls cost, but I would think one of those would last at least three or four years, if not 10. Plus there would be very little waste.

At any rate, I never sat down and did the math, but I know this fall ritual ends up saving me money. (All I remember was that my gas bill was dramatically lower the first year I did this, without making any other changes.) If the potential really is 30 percent, I think I'll do the newer windows next weekend to try to squeeze out a little more.