Window Film Basics: Heat Loss Reduction
Facts about Heat Loss
The most accurate measure of heat loss is the U Value. This value measures the rate that heat escapes through a window and is expressed in BTU’s 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 BTU’s are being lost through the window.
Here’s how it works:
1/4″ single pane glass has an average U Value of 1.06. This means that 1.06 BTU’s per square foot per hour escape through the glass.A window of 10 square feet is losing around 10.6 BTU’s per hour. If it is 70 degrees inside & 40 degrees outside, the heat loss is now 318 BTU’s(10.6 x 30 degrees) per hour.
Now multiply this by all the rooms in your house times 24 hours a day. We’re talking about thousands of BTU’s a day! Your heater has to keep up with & replace all of this heat.
Solar Control Plus “Low E” film can reduce heat loss substantially
3M Solar Control 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. 3M’s LE35AMARL Medium Amber window film installed on single pane glass lowers the U Value of the glass from 1.06 to 0.74. This represents a reduction in actual BTU’s lost of 30%. It also means that you are saving a lot of 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 BTU’s per hour is actually fairly small. Therefore, the payoff on these film types for this type of glass is fairly long.