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As the weather turns colder with the winter months, we start getting calls for window film that will help keep heat inside a home. It’s a common enough question, that it warranted a blog post – so here we go!
Window film that seeks to retain heat in the home during winter is called sold as low-E window film. It is different from the majority of window film on the market that is made to control the sun’s energy from entering a home. This film seeks to prevent heat from your HVAC system from leaving a home.
Low-E (low emissivity) window film is a type of window film that is designed to improve the energy efficiency of windows in residential and commercial buildings. (Read more about emissivity here.) It works by reducing the amount of heat transfer through windows, thus helping to maintain a more consistent indoor temperature, and reducing the reliance on heating and cooling systems. Here’s how it works:
Low-E window film is coated with a microscopically thin layer of metal or metal oxide. This coating is virtually invisible to the naked eye. It reflects a significant portion of the infrared radiation (heat) from the sun while allowing visible light to pass through.
During the colder months, Low-E film reflects heat back into the interior space, preventing it from escaping through the windows. This can help keep your home warmer and reduce heating costs.
In the summer, Low-E film helps to block a portion of the sun’s heat from entering your home, reducing the need for air conditioning, and keeping your indoor spaces cooler. Typically, the amount of summer heat rejection is considerably lower than with a straight solar control film.
Many Low-E films also provide UV (ultraviolet) protection, which helps prevent the fading of furniture, flooring, and other items by blocking harmful UV rays.
There may be others, but the main manufacturers who offer a low-E film product are 3M, Llumar, and Solar Gard. Concord Window Film does not manufacture a low-E film at this time.
If you are going to invest in low-E film, you’ll want to know how much of an impact it will have on your comfort. We calculated the reduction in U-value from several film manufacturers and found you can reduce the U-value of your windows with a low-E film by about 30%.
It’s important to note that these statistics are calculated based on film being applied to clear glass windows. A lot of windows sold in the colder zones of the U.S. now are not clear but are treated with a low-E coating already. These low-E windows already have a very low U-value of around .34 (compared to a standard dual pane window which is around .5). The amount of benefit you will get from adding low-E film to low-E windows is not reported by any manufacturer.
Currently, homeowners can only purchase low-E film through an authorized installer of one of the manufacturers who supplies the film. So to date, there is no manufacturer that will sell the film directly to homeowners.
If you are looking for a window film that will help you prevent heat from escaping from your home in the winter, you’re only option is to go to a manufacturer who makes a low-E film and have it professionally installed.
Things to note are that if you already have low-E glass in your windows (a professional installer should be able to tell you if you do) it is not known how much benefit you will get from installing a low-E film.
