Vinyl Windows Part III: Low E Coatings and Inert Gas

The previous post covered the manufacture of thermal panes and how they work, but there are two key components that deserve more attention: the Low-E coating and the inert gas between the panes. While invisible, these elements are critical to the exceptional energy efficiency of thermal panes.

Low-E Coatings

The Low-E (low emissivity) coating is a thin metallic layer applied to the glass in a thermal pane. This microscopically thin metal or metallic oxide layer acts as a filter, separating different wavelengths of light. It blocks long wavelengths, or heat, while allowing shorter wavelengths of visible light to pass through.

When applied to the exterior glass of a thermal pane, the Low-E coating keeps heat out during summer. On interior glass, it reflects heat back into the home during winter, enhancing year-round comfort and reducing energy consumption.

In double- or triple-glazed thermal panes, the Low-E coating can be applied to multiple panes. This allows manufacturers to customize glass packages for different climates. Adding more Low-E coatings within a thermal pane significantly boosts energy efficiency and comfort, making these windows an excellent choice for homeowners looking to reduce heating and cooling costs.

Inert Gases

Inert gases, such as krypton and argon, are used as insulating fills between the panes of glass in thermal panes. While both gases enhance energy efficiency by reducing heat transfer, they have distinct characteristics:

• Argon Gas: Less dense than krypton, argon provides moderate thermal performance. However, it is abundant and inexpensive to produce, making it a cost-effective option for most homeowners.
• Krypton Gas: Denser than argon, krypton offers superior thermal performance, particularly in triple-glazed thermal panes with smaller gaps between the glass. However, krypton is rarer and more expensive to produce. For homeowners with a higher budget, krypton-filled panes offer unmatched energy efficiency.

Choosing between argon and krypton depends on the homeowner’s budget and desired level of thermal performance. Both options improve the overall energy efficiency of thermal panes significantly.

The ER Rating

Understanding a window’s energy efficiency can be overwhelming due to the technical metrics involved. Below are some key terms, as outlined by Natural Resources Canada:

• U-factor: Measures the rate of heat transfer from warm to cold areas, expressed in watts per square meter Kelvin (W/m²K) or British thermal units per hour per square foot Fahrenheit (Btu/h × sq. ft. × °F). Lower numbers indicate higher efficiency.
• Solar Heat Gain Coefficient (SHGC): A ratio that shows how much solar heat passes through the window. Higher numbers mean more solar heat gain.
• R-value: Indicates resistance to heat transfer, measured in square feet per hour in degrees Fahrenheit per British thermal unit (sq. ft. × h × °F/Btu). Higher values mean better performance. Although not part of energy performance standards, R-values are often used by contractors.
• Visible Transmittance (VT): A ratio showing how much visible light passes through the window. Higher numbers indicate more light.
• Centre-of-Glass Rating: Refers only to the energy efficiency of the glass portion, excluding the window frame and other components.

To simplify this data for homeowners, the ER rating (Energy Rating) was developed. This unitless measurement combines all the above factors into a single value, where a higher number indicates greater energy efficiency. Homeowners can use the ER rating to easily compare window options based on performance and cost, ensuring they choose the best windows for their budget and needs. Quality Homes & Renovations can help you make the best choice for windows on your home, whether replacement or a new build.