Facts About Heat Loss

The most accurate measure of heat loss is the U Value.  It measures the rate that heat escapes through the windows and is expressed in BTUs per square foot per hour per degree Fahrenheit.  It is affected by both the physical properties of the material and the difference in temperature on both sides of the glass.  A lower U Value means fewer BTUs are being lost through the window.

Here's how it works.

¼" clear single pane glass has an average U Value of 1.06.  This means that 1.06 BTUs per square foot per hour escape through the glass.

A window of 10 square feet is losing around 10.6 BTUs per hour.  If it is 70° inside and 40° outside, the heat loss is now 318 BTUs (10.6 X 30°) per hour.

Now multiply this by all the rooms in your house times 24 hours a day.  We're talking about thousands of BTUs a day.  Your heater has to keep up with and replace this lost heat.

3M Scotchtint Plus "Low E" film can reduce heat loss substantially.  As with every other measure, we compare the performance of the filmed glass to the glass itself.  LE35AMARL Medium Amber installed on single pane glass lowers the U Value of the glass from 1.06 to .74.  This represents a reduction in actual BTUs lost of 30%.  It also means you are saving a lot of the money you spend to heat your house in the winter.

Similar savings can be realized on thermal pane windows, but since they are much more efficient than single pane windows, the actual improvement is smaller, most often on the order of 15% - 20%.

This may sound like a lot, but the actual savings in BTUs per hour is actually fairly small.  Therefore, the payoff of these films on this type of glass is fairly long.