We're getting the first serious wintery blast here in Central Texas, and the heat sources we count on were running continuously. We have an oil-filled radiator heater and a small space heater for our 420 square foot efficiency apartment.
I suddenly realized that we hadn't insulated the windows like we have in the past, so I got out some bubble wrap and insulated the 3 generous windows we have. Within 30 minutes the space heater was cycling off and we were toasty warm.
Years ago, we lived in Don's mom's old house, approximately 2000 sq. ft., with leaky floors, walls and windows--single pane windows. One winter, in desperation, I insulated the windows with bubble wrap. The next month, a colder month, our electric bill went down over $70. It worked so well we left it up for the next 3 years, then peeled it off and replaced it. It works well for cooling, too.
It's easy to do. Just cut out bubble wrap to the size of the window-you can patch. Spray the window with water and press the bubble side to the glass. It will adhere on its own. If it comes loose, spray a little more water and stick it back up. Step two? There is no step two, that's it.
Now compare the cold radiating into the room from another window to that one, then go scrambling for some more bubble wrap.