How Low-E Film Can Save Energy and Your Home

Sun shining in window behind flower in glass

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With the sun beating down on your house, heat and ultraviolet rays (UV) can enter through the windows. UV rays and solar heat can make a house hotter and can damage many of your belongings.

Buying windows with embedded coatings is one way to mitigate the heat and damage. But if your windows do not have these coatings or if you want to supplement these coatings, you may decide to add low-E film to the windows.

What Is Low-E Film?

Low-E film is a coated plastic film, available in rolls, which sticks to the insides of your windows to block or slow the transmission of UV rays. Low-E means "low-emissivity." Low-E films usually contain metal or metal oxide as the material that counteracts the UV rays.

Manufacturers often state that low-E films reflect between 70- and 80-percent of solar heat gain in the summer or conserve over 50-percent of interior heat in the winter.

If you aren't prepared to replace your old windows with new, energy-efficient windows that feature factory-applied low-E coatings, applying low-E film can be a viable, cost-saving alternative.

Applying low-E film can be a do-it-yourself project if you have small windows. If you aren't experienced at installing films or if you want to ensure a perfect fit, you may want to hire a professional.

Low-E Film For Different Climates

Before purchasing and installing low-E window film, consider the climate where you live and the orientation of your windows.

Look at the packaging of the window film for the solar heat gain coefficient (SHGC) and the visible transmittance rating (VT). If you live in a cold climate, look for a high SHGC rating or a lower rating if you live in a warm climate. Products with higher VT ratings admit more natural light.

Low-E Film Protects House and Belongings

Aside from reflecting heat, the low-E film also reduces glare within a room and increases privacy without compromising the view.

These films also block around 99-percent of UV rays, which can damage or fade furniture, upholstery, flooring, and artwork. This can be an important benefit for preserving the resale value of your house. While some of the items that low-E protects are personal and are not part of the house, other items such as flooring are permanent and expensive to repair or replace.

Low-E Film Pros and Cons

Pros

  • Blocks up to 99-percent of UV rays.
  • Reduces solar heat gain.
  • Protects house and belongings by limiting their exposure to UV rays.
  • Most low-E films on the consumer market are easy to apply.
  • Some low-E films can be removed easily, with no residue left on the window glass.

Cons

  • Low-E film creates a slight tint to your windows, which can impair visibility or block too much light so that you have to rely more on electric lighting.
  • While easy to apply, low-E films can be difficult to apply flawlessly.
  • Some films appear mirror-like from the exterior of your home.
  • Houseplants may suffer from inadequate lighting when placed near a window with the low-E film.
  • Since they only cover the glass portion of your windows and not the frames, unlike certain films, low-E films do not cut down on drafts. Instead, use caulk or weather stripping to insulate and tighten your home's envelope.
  • Some films can easily be removed, while others are more difficult to remove.
  • Application of low-E film can void your double-pane window manufacturer's warranty, as they cause the interior pane of glass to expand at a different rate than the exterior pane, which can potentially cause cracking.

Low-E Film Alternative

Low-E films found on the consumer market tend to be easy to apply and remove. However, it can take time to apply the film well, so that no bubbles develop. It can also be tricky to keep the edges and corners down.

One alternative is to install window insulation film. Window insulation film is applied to the window trim, not to the glass, thus leaving an insulating space between the film and the glass. Heat from a hairdryer helps to tighten the film and make it more air resistant.

Window insulation film is virtually clear, so your view is not compromised. Creases and waves may develop in the film over time. But these often may be straightened out by re-applying the film or by heating it again with the hairdryer.