first you want to tape clear plastic over the windows sealed around the sides of the frame. This will create a sealed air gap to reduce heat loss at the window. Then add the black plastic that is away from the clear plastic by about 1 inch. This will greatly increase the efficiency of the black plastic heat collector. Just remember to keep the open air space between the black plastic and clear plastic as mentioned above.

A lot depends on where you live. I had a friend who was complaining of the cold in his apartment which was old and the heat was included in the rent (and he had no control over it). I suggested he put an additional plastic window over his windows. Kits of pre-cut plastic are available. When he did it raised the temperature from 65 to 74, a big difference. Of course this was an old building with single frame windows. Modern windows often have double pane or even triple pane glass. I have double pane and still find that add addition layer of plastic helps.

A simple trick to help lower heating costs is to use a black trash bags and tape or thumb tacks, and place it up on the inside of a south side window. The side the sun shines on. This will attrect more heat than a clear window and trap it inside the home. Its best if a slite clearnce is left between the window and the bag. This will allow air to inter from the bottem and come out the top as hot air. A small empty can, like a tuna can, or a part of a cardboard roll from the toliet paper roll will work. Only about a 1/2 inch peace is needed. Place it between the window and the plactic bag, to allow the air to inter the bottem and escape the top.

This will help increses the room tempature. It raised the tempature in my house about 2 degrees per bag. I have 9 bags on 7 windows. In the bedroom I put up 2 bags per window and rased the tempature about 6 degrees. I covered both windows completely. This also helps keep the heat in. It adds one more barrer the heat has to go through to escape.