Buying new windows involves making many choices. Windows come in all shapes and sizes and can be made from a range of materials. One of the many choices that homeowners must make when selecting a new window is what type of glass to use.
There are many different types of window glass. The type of glass you pick for your windows can affect their functionality, their energy efficiency, and their appearance. Knowing the kind of window glass available can help you make your decision during the window buying process.
Here is what every homeowner should know and what we will cover:
- What Types of Glass are Used in Windows?
- What Type of Glass is the Best?
- How Does Glass Type Help to Control Climate?
What Types of Glass are Used in Windows?
There are many types of glass found in modern windows (1).
Float Glass and Annealed Glass
Float glass is the basic type of glass in most modern windows. Float glass takes its name from a process wherein large, flat panels of molten glass are passed into a molten tin. The result is a very flat, even type of glass. Other types of glass typically start out as float glass and are then treated to produce different results (2).
Typically, float glass is annealed for strength. Annealed glass is float glass that has been slowly cooled. It is then used to create other types of glass like tempered glass, laminated glass and so on. When annealed glass breaks, it breaks into large, sharp shards. Annealed glass is ordinary window glass, before it is coated or treated for strength or energy efficiency.
Heat Strengthened Glass
Heat strengthened glass is annealed glass that been reheated and cooled rapidly. Heat-strengthened glass is twice as strong as annealed glass. When heat strengthened windows break, the shards can be sharp and may cause injury (3).
Tempered glass is float glass that has been heated to about 1200 degrees Fahrenheit and then rapidly cooled. The rapid cooling of the glass causes the inner core to remain liquid while the outer core becomes solid and strong. When the inner core finally solidifies, the result is an equal amount of tensile and compressive stresses across the sheet of glass (4).
Tempered glass is very strong and when it breaks, it breaks into very small, dull pieces. Tempered glass is also called safety glass and is found in car windows.
Heat Soak Tempered Glass
Heat soak tempered glass is glass that has been specially heated, forcing unstable elements in the glass to expand and break. This helps the manufacturer catch and discard any pieces of glass that are not stable enough to use in real-world situations. Heat soak tempered glass adds an extra level of safety to glass that must be extra strong in order to be safe to use (5).
Laminated glass is glass that is made by fusing two pieces of glass with a clear plastic inner core. Laminated glass is a type of safety glass that does not easily break, and when it does, it typically stays in the frame. Laminated glass is often used in windshields to prevent flying objects from hitting the driver or passenger (6).
Insulated glass is made from two or more pieces of glass with an air-filled space in between. The air in between the two sheets of glass provides insulation that can help keep cool air in the home and warm air out of the home, or the reverse. Insulated glass comes in double and triple pane varieties, with triple pane glass providing more insulation than double pane (7).
Gas Filled Glass
Gas provides better insulation than air. Insulated panes that are filled with argon or krypton are referred to as "gas filled." Argon is a more common choice than krypton because it works well and is inexpensive. Krypton is a better insulator than argon but is far more expensive. The additional expense of krypton makes it far less popular among homeowners seeking insulated glass (8).
Low-e coating is made from an invisible layer of metallic oxide. This coating helps deflect UV rays, keeping heat out of the house during the summer. Low-e glass also helps keep heat in the home in the winter. Low-e coatings are useful for controlling temperature and can prevent furnishings, carpeting and hardwood from fading over time from direct sunlight. Many homeowners combine low-e coatings with other types of glass, like insulated glass, to make the glass even more energy efficient (9).
This feature absorbs heat from the sun to prevent it from entering the home. Tinted glass can help reduce solar heat gain coefficient (SHGC), glare and visible transmittance. The color of heat-absorbing tint that a homeowner chooses for his or her windows often depends on climate and other factors. For example, black-tinted glass is not recommended in hot climates because it absorbs a greater amount of light than heat. Some homeowners in hot climates prefer blue- and green-tinted windows because they provide a greater penetration of visible light (10).
Obscured glass is glass that has been frosted or patterned so that light is allowed to filter in, without distinct shapes being seen through the glass. Obscured glass is commonly used in bathrooms to allow natural light into the room while preventing anyone outside the home from seeing the inside (11).
What Type of Glass is the Best?
The type of glass that's best for your home depends on a number of factors including:
- Type of window being installed
- Energy efficiency priorities
While annealed glass is the standard window glass commonly found in homes, many property owners seek to install windows that can offer extra benefits.
Homeowners who want to save money on utilities, for example, may choose to install insulated, gas-filled glass with a low-e coating. This type of glass makes it easy to control the amount of heat entering or escaping the home.
In contrast, homeowners who want to control the visible light that enters their home may opt for tinted windows. Since each homeowner has his or her own priorities, the type of window that is best depends entirely upon the homeowner (12).
How Does Glass Type Help to Control Climate?
In homes with annealed glass windows (which transmits heat easily), sunlight in summer can cause the home's interior to heat up on hot days. Under these circumstances, the air conditioner must work much harder to keep the home cool. In winter, single-pane annealed glass allows heat to escape the home, making it harder to keep the home warm.
Special coatings and glass insulation can prevent this heat loss or heat gain. The most energy efficient windows have a low-e coating and are triple-paned with a krypton-filled core. However, these windows are very high in cost. The more affordable and still very energy efficient windows have a low-e coating and are double-paned with an argon-filled core.
The US ENERGY STAR program estimates that installing energy efficient windows in your home can save hundreds of dollars on heating and cooling bills every year (13).
Homeowners who choose to install less efficient types of glass in their windows may need to put extra effort into controlling their interior climate. Closing blinds to block the sun and installing weather stripping at the right times of year can save the homeowner money while also preventing the home from becoming uncomfortable inside.
Even with these precautions, many homeowners will still spend extra money on heating and cooling costs if their windows are not made from energy-efficient glass (14).