What Are Low-E Windows?

April 6, 2016

What Are Low-E Replacement Windows?

Low Emissivity coating, commonly referred to as “Low E” is an optional feature you will find offered by many replacement window companies. While each window company may have their own spin or name for this feature, the basic functionality of Low-E is the same for all.

What is Low E?

Low-E is a micro coating that is applied during the glass manufacturing process that assists in filtering out ultraviolet and infrared light that pass through your windows. Windows with this feature offer a significant thermal and energy-saving advantage, and often boast the Energy-Star certification.

Ultraviolet and Infrared Light

Ultraviolet and Infrared light from are what cause your furniture to fade, and your home to get warm regardless of the outside temperature. When the sun glares down on your home, UV and IR rays beam through your windows and penetrate every surface in reach. When the surfaces inside your home are hit by these rays, uncontrolled temperature changes usually result at the most undesirable times.

Both of these forms of light are usually undesirable as they cause deterioration and unmanageable heating.

How much does it cost?

Low E is generally an affordable upgrade at $30-$70 per window. Cost may vary depending on the window manufacturer, the number of glass panes, and the size of the window. Low E Patio door glass is also available, usually at an upgrade cost of $75-$150.

Why do I need it?

Many contractors skip the investment of Low-E glass to cut costs on their building project. Since Low-E is not a visual feature of the window, it is often overlooked by those buying or remodeling a home.

If you plan to live in the home that you are replacing windows for, the energy-saving advantages of Low-E are worth the investment alone. In addition to lower utility bills, you will feel a comfort difference with the consistency of heat that your home sustains. The colors in your home will stay vibrant as Low-E protects your furniture, carpet, and paint from the harmful rays of the sun.

Is it worth the investment?

If energy saving and comfort are reasons for your window replacement, then Low E glass is most definitely worth the extra investment.

The overall energy consumption of your home is dependent on many factors including insulation, siding material, efficiency of your roof, and the efficiency of your HVAC system. On average, windows and doors account for 18-20% of the energy lost in a home. Depending on the severity of your current heat loss via your windows, Low-E coating coupled with an energy-efficient window frame could impact your energy consumption by this much.

Types of Low E

Many window companies offer varying intensities of Low-e glass to best fit the needs of multiple climates. For very sunny climate zones, low solar-gain low-e may be desired to prevent the maximum amount of infrared radiation. However, in colder climates, a high solar-gain low e may be desired as some controlled light can assist in heating and overall energy savings.

To best understand which low E is right for your home, refer to the Energy Star guidelines for your climate zone.

Spectral transmittance curves for glazings with low-emittance coatings (Source: Lawrence Berkeley National Laboratory).

Can I apply Low E to my existing windows?

Some aftermarket tinting options help in filtering out the same radiation as Low-E coatings. It is important to note that these after market films are not a part of your glass, leaving them susceptible to peeling and scratching over time.

If the other components of your window are already efficient, using chambered and foam filled vinyl, then a tinting solution may be a more affordable option. However, tinting a structurally inferior window will likely not result in significant energy savings.

Does it change the color of the window?

Depending on the intensity, Low E Coating can make the window appear slightly darker. This effect is not to the intensity of window tint or sun glasses, but can be noticed when comparing to a completely-clear glass.

How do I know if I have low E now?

You can test your current glass with a heat lamp or other significant heat source. Shine the source through one side of the glass, and hold your hand a few inches from he glass. If you can feel significant heat transfer, then it is not likely that your windows have a low emissivity feature.

Measuring Emissivity

Every major window manufacturer elects the non biased National Fenestration Ratings Council to independently test and rate each window. This testing is represented by a table that should be on the glass of every new window. The NFRC label states four key metrics. The Visible light transmittance and Solar Heat gain coefficient metrics are the most important when comparing one Low E window versus another.

Click here to read more about using the NFRC label to help you decide the best replacement window for your home.