Low emissivity glass (low-e), how does it work?

If you are selecting windows for new construction or replacing existing windows, it’s important to choose the most efficient windows you can afford that work best in your climate. Energy efficient windows are an important consideration for both new and existing homes. By installing low emissivity (low-e) energy-efficient glass, you reduce heat loss through windows, make your home more comfortable and save money on energy bills.

But it is not only money you are saving by choosing energy-efficient glass for your windows, you also reduce your home’s CO2 output, making it’s carbon footprint smaller and more environmentally friendly.

So, what is low-e glass? In this article, we provide you with an in-depth overview of Low-emissivity (or Low-e) glass and their coatings.

What is low-e glass, and is it right for your home? To help you decide, this article discusses what homeowners should know before investing in new windows.

What is Low-e glass?

Low-emissivity or low-e glass is a type of energy-efficient glass that is designed to prevent heat from escaping to the cold outside environment through your windows. Low-e glass has a thin, transparent coating of tiny metal oxide layers that drastically reduces heat transfer and reflects the internal heat back into your room.

The coating is not visible to the naked eye, allowing as much natural light as possible to enter the house. However, even if it is transparent, this coating protects your home from unwanted UV rays (UV rays) that can harm your skin, fade your carpets and wall coverings and damage your furniture. In addition, it helps control the radiant heat (infrared light) that enters and exits a room. In other words, it keeps your home warmer in the winter and cooler in the summer. This saves money by reducing heating and cooling bills, while creating a comfortable living environment.

low-e coating on glass surfaces keeps your home’s interior warmer in cooler months and cooler in warmer months

In order to understand how low-e glass works, we can compare it with a thermos. Both function in the same way. A thermos has a silver lining, which reflects the temperature of the drink it contains. The temperature is maintained because of the constant reflection that occurs, as well as the insulating benefits that the air space provides between the inner and outer shells of the thermos, similar to an insulating glass unit. Low-e glass works the same way since it is comprised of extremely thin layers of silver or other low emissivity materials. The silver low-e coating reflects the interior temperatures back inside, keeping the room warm or cold.

Low-e glass is essential for rooms or buildings with a high proportion of windows or glass doors, such as living rooms, offices and sun rooms. The use of low-e glazing helps to retain heat even in winter, allowing you to comfortably use these rooms for more months of the year. Low-e glass is also recommended for north or east facing windows, where a larger proportion of heat loss is expected. For south and west facing glazing where overheating can become a problem in the summer months, it is recommended to use solar control low-e glass.

What about summer?

Low-e glass windows not only keep the heat in during winter, they can also reflect it back out during summer. They literally pick out and refuse entry to certain portions of the light spectrum. Therefore, they allow less infrared light (radiant heat) to enter the house, keeping it cooler during the summer months  thus reducing operating costs related to air conditioning.

Low-e coating types 

There are actually two different types of low-e coatings: passive low-e coatings and solar control low-e coatings. Passive low-e coatings are designed to maximize the solar heat gain of a home or building creating a passive heating effect and thus reducing reliance on artificial heating. Solar control low-e coatings are designed to limit the amount of solar heat passing through them thus keeping buildings cooler and reducing energy consumption related to air conditioning.

Where is it?

The metallic oxide layer is applied to a few different areas. If it is a soft coating, it will be on the inner surface of the glass. Soft coatings are actually very efficient in their reflex capabilities, making the windows energy efficient at a very high rate. However they can’t operate under extreme physical conditions so they have to be placed on the inside of the glass. Hard coatings are less efficient but can withstand weather conditions and are therefore usually located on the outside of the windows. However, the most common area of ​​application is between the two glass surfaces of a double-glazed window. It is not actually a coating but a thin sheet suspended in the middle of the glass panes. So it works not only as a low emission window, but also as a form of thermal insulation against airflow and heat loss. In other words, this sheet can effectively convert a double glazing into a triple glazing and this insulation can be further supplemented by the addition of inert argon gas for even higher R-value. The glaze acting as an insulator, it traps the warmth in a building, reduces energy bills and keeps the glass constantly warm, which reduces condensation buildup on icy days of the year.

Who do i ask?

Low-e windows are definitely worth the investment. They almost come standard now, but if you’re remodeling an older house, these glazes can save you a lot of money.

You may have the option of replacing the windows in their existing frame; discuss this option with your window retailer and installer to find out if it will work for you. Many older double glazed units do not contain low-emissivity glass and are therefore not energy-efficient. By replacing your existing window glass with low-e glazing, you can improve the energy efficiency of your home, reduce your monthly bills and decrease the size of your carbon footprint. Low-e glazing units can make your home more than twice as energy-efficient in comparison to older double glazing with no low-e coating.

There are all kinds of efficiency codes and they all vary depending upon your particular environment. So as you investigate low-e glass window coatings and films, you’ll definitely want to hire a professional who can not only install the new units but can also give you advice about which models will work best for your specific area in terms of durability, application, location, strength, and overall efficacy.

Selection process

In colder climates, consider selecting glass with passive low-e coatings to reduce heat loss. In warmer climates, select glass with solar control low-e coatings to reduce heat gain.

In addition to choosing the window type, you also need to consider labeling, warranties and proper installation.

First look for the energy certificate with indicators and classifications when buying new windows. Glazing that carry the Certified Passive House Component seal has been tested according to uniform criteria; they are comparable in terms of their specific values, and are of excellent quality regarding energy efficiency.

Even the most energy-efficient glass must be properly installed to ensure energy efficiency and comfort. Have your windows installed by trained professionals according to manufacturer’s instructions; otherwise, your warranty may be void.