The short answer is yes, you can put window film on Low-E glass, but it requires careful consideration and the right type of film. Using the wrong film can lead to glass breakage due to thermal stress, rendering your energy-efficient windows useless. This article provides a comprehensive guide to understanding the potential issues and how to apply window film safely and effectively to Low-E glass.
Understanding Low-E Glass
Low-E, or Low-Emissivity, glass is designed to minimize the amount of infrared and ultraviolet light that can pass through your windows without reducing the amount of visible light. This is achieved through a thin, virtually invisible coating on the glass surface, which reflects radiant heat, helping to keep your home cooler in the summer and warmer in the winter. The coating’s location – whether it’s on surface #2 (interior side of the outer pane) or surface #3 (exterior side of the inner pane in a double-pane window) – significantly impacts the glass’s thermal performance and its sensitivity to window film application.
Types of Low-E Coatings
There are primarily two types of Low-E coatings: passive Low-E and solar control Low-E. Passive Low-E coatings primarily reduce heat loss, making them ideal for colder climates. Solar control Low-E coatings, on the other hand, are designed to reduce heat gain, making them more suitable for warmer climates. Knowing which type of coating your windows have is crucial before applying any window film. Contacting the window manufacturer or a professional installer is the best way to determine this.
The Thermal Stress Factor
The primary concern when applying window film to Low-E glass is thermal stress. Window film, particularly darker or reflective films, absorbs a significant amount of solar energy. This absorbed energy heats up the glass. With Low-E glass already reflecting a portion of the solar radiation, adding film can increase the amount of heat retained by the glass. This can create a temperature differential between the center of the glass pane and the edges, which are typically cooler due to being framed. This differential leads to stress, and if the stress exceeds the glass’s tolerance, it can crack.
Navigating Window Film Application on Low-E Glass
The key to successfully applying window film on Low-E glass lies in selecting the correct film type and, ideally, having it professionally installed.
Choosing the Right Film
“Low-E compatible” window films are specifically designed to minimize the risk of thermal stress. These films typically have a lower solar absorption rate and a higher visible light transmittance (VLT) compared to standard window films. This means they allow more visible light to pass through while absorbing less solar energy, reducing the potential for overheating. Consult with a reputable window film manufacturer or installer to determine the best film for your specific Low-E glass type and climate.
Professional Installation vs. DIY
While DIY window film kits are available, professional installation is highly recommended for Low-E glass. Professional installers have the experience and tools to properly assess the glass type, select the appropriate film, and apply it correctly. They also typically offer warranties against glass breakage due to film application, providing peace of mind. DIY installation can void the window manufacturer’s warranty and increase the risk of glass damage.
Testing the Compatibility
Before applying film to all windows, consider a test application on a small, inconspicuous area. Monitor the glass for any signs of stress, such as cracking or discoloration, for several weeks. This allows you to assess the compatibility of the film with your specific Low-E glass without risking widespread damage.
Frequently Asked Questions (FAQs)
Here are some frequently asked questions about applying window film to Low-E glass:
1. Will applying window film void my window warranty?
Yes, in many cases, applying non-approved window film will void your window manufacturer’s warranty. Check your warranty documentation carefully before applying any film. Some manufacturers may approve specific types of film, so it’s worth contacting them directly.
2. How can I tell if my windows are Low-E glass?
Look for a Low-E label or sticker on the window frame or glass itself. You can also try a simple test: hold a lit match or lighter in front of the glass. If you see four reflections and one is a different color than the others, you likely have Low-E glass. Contacting the window manufacturer is the most reliable method.
3. What types of window film are safe for Low-E glass?
Low-E compatible films with a high VLT and low solar absorption rate are generally considered safe. Neutral-colored or lightly tinted films are often a better choice than darker, more reflective films.
4. Can I put window film on both sides of my Low-E glass?
Applying window film to both sides of Low-E glass is generally not recommended due to the increased risk of thermal stress. Focus on applying film to the exterior-facing side only, if applicable.
5. What are the benefits of using window film on Low-E glass?
Even with Low-E glass, window film can provide additional benefits, such as reduced glare, increased privacy, protection against UV damage to furniture and flooring, and enhanced security (safety films).
6. How long does window film typically last?
The lifespan of window film varies depending on the type of film, the quality of installation, and environmental factors. Generally, expect window film to last between 5 and 15 years.
7. What are the signs of thermal stress damage on Low-E glass?
Signs of thermal stress damage include cracking, particularly near the edges of the glass, as well as bowing or warping. In severe cases, the glass may shatter.
8. How much does it cost to have window film professionally installed on Low-E glass?
The cost of professional installation varies depending on the size and number of windows, the type of film, and the installer’s rates. Expect to pay between $5 and $15 per square foot.
9. Can I remove window film from Low-E glass without damaging it?
Removing window film requires careful technique and the right tools. Using a heat gun or steamer can help soften the adhesive. A plastic scraper can then be used to gently peel off the film. Residue can be removed with a specialized adhesive remover. Professional removal is recommended to avoid damage.
10. Are there any specific climates where window film is not recommended for Low-E glass?
In extremely hot climates with intense sun exposure, the risk of thermal stress is higher. Carefully consider the type of film and consult with a professional installer to assess the suitability of window film for your specific location.
11. What is the difference between dual reflective and non-reflective window film and which is better for Low-E glass?
Dual reflective film has a reflective coating on both the interior and exterior surfaces, providing better heat rejection. Non-reflective film only has a coating on one side. Non-reflective films are generally safer for Low-E glass because they absorb less heat. However, Low-E compatible dual reflective films exist and can be used if carefully selected and professionally installed.
12. What should I ask the window film installer before hiring them to work on my Low-E windows?
Ask about their experience working with Low-E glass, their understanding of thermal stress, the types of film they recommend, their warranty policy, and their insurance coverage. Get references and check online reviews. Ensure they perform a thorough assessment of your windows before providing a quote.