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Energy Efficient Windows

3.9 based on 56 ratings

Updated on Sep 05, 2013

Have you ever wondered why rooms with thick curtains tend to stay warmer in the winter? If you’re interested in reducing your family’s carbon footprint or simply want to help your folks save a little money, then knowing how to insulate your windows is really important! Which type of window covering will keep a room the warmest?


Which model window solution will keep a room the warmest?


  • Four small square cardboard boxes of the same size
  • Four 1-liter bottles of water
  • Four inexpensive thermometers
  • Plastic wrap
  • Thin curtain material
  • Heavy, insulated curtain material
  • Ruler
  • Pencil
  • Scissors
  • Tape
  • Small funnel
  • Double-sided sticky tape
  • Duct tape or packing tape
  • Cooking pot
  • Stove
  • Water
  • Notebook and pen


  1. Cut a large “window” into the same side of each of three of the cardboard boxes. Each window should be the same size, so you'll want to use the ruler to measure and mark with a pencil before cutting. Do not cut a window in the fourth box—this box will model a room that has no windows.
  2. Cover the inside of your windows with plastic wrap, taping it into place on the inside of the box.
  3. Cut curtains from the two types of curtain material that will completely cover your plastic wrap window. Secure the thinner curtain material in place with double-sided sticky tape over the inward-facing surface of one of the box’s windows. On the next box’s window, secure the heavier insulated curtain material in the same way. For the third box, leave the plastic wrap window unadorned.
  4. Pour the bottles of water from the plastic bottles into the pot and ask a parent to bring the pot to a boil. Allow the water to cool slightly so it won’t scald if it splashes on you.
  5. With your parents’ help, use the funnel to pour the hot water back into each of the bottles so that about the same amount of water is in each bottle. Some water may have evaporated when you boiled it, so the bottles will not be completely full.
  6. Insert a thermometer into each bottle and record the temperature reading in your notebook.
  7. Remove the thermometers from the bottles.
  8. Place each bottle into a box and seal each box closed with duct tape. Leave the boxes outside in the evening, preferably at a time when the sun is setting. Remember, we’re trying to determine how much heat each box loses, so we don’t want the boxes to cook in the sun.
  9. After three hours, open the boxes and take a temperature reading for each of the bottles. Remember to record the results each time you take a reading.
  10. What do you notice about how long the bottles stay warm? Which boxes are more efficient than others at keeping the heat inside the bottle?


Any type of window allows heat to escape, so the box without any window at all should have retained the most heat. However, for the boxes with windows, a heavier fabric helps retain heat better than a thinner one. The box with no curtain should have lost the most heat.


Insulated curtains are more energy efficient than curtains made of regular material. Why? One of the ways heat travels is through conduction, when heat moves from a warmer area to a cooler one. However, thicker materials are better insulators—that is, they tend to prevent conduction from occurring as rapidly. Interestingly enough, the best insulator is nothing at all, because heat can’t travel by thermal conduction through a vacuum! That’s why manufacturers of insulated food and beverage containers often nest two flasks together and suck all of the air out of the space in between. Heat is only able to effectively leave via conduction through the top of the container, and only a little is lost through the sides due to minimal conduction and some thermal radiation.

So how much less energy might the average household use by adding thermal curtains to heated rooms? Is the cost of insulated curtains worth it if you weigh it against the money you might save? Thermal curtain manufacturers estimate that homeowners can save up to 25% on their home’s energy bill, and the US Department of Energy recommends that homeowners use insulated curtains to save money. Can you find any other methods to help save some money on your family’s energy bill? Use your creativity, and apply what you’ve learned about heat and heat conduction!