More Than A View: Understanding Window Energy Efficiency


Energy efficient windows will keep your home warmer in the winter by reducing drafts and holding in heat. In summer, they help keep the heat out. Quality windows contribute to reduced energy usage, cutting annual energy costs by up to 20%.

But not all windows are created equal, so it’s important to learn a bit about how to evaluate the energy efficiency of a window before you set out shopping.

Here are a few of the things to look out for when it’s your turn to go window shopping.

Materials: The most common types of window frames are wood, vinyl (PVC), and aluminium. Wood frames are energy efficient, but can be expensive to purchase and need regular upkeep. Aluminium frames are inexpensive but not as energy efficient. Vinyl frames are less expensive and can be quite efficient.

Low Conductivity Spacer Systems: Spacers are used between the layers of glass in a window, to hold them together at the required distance. Conventional spacers were made from aluminium, but they provided poor thermal insulation. New spacer products have been developed from materials with a low conductivity rate and high thermal efficiency such as fibreglass, vinyl and others.

Glazing or Coating Systems: Low-e stands for low-emittance coating. Microscopically thin layers of metal or metallic oxide are coated onto the window glazing. Different types of coating have different properties, but all are designed to lower heat flow through the window.

Seals and Weatherstripping: Weatherstripping reduces air leakage by creating a tight seal between windows and the building structure. Choose a type of weatherstripping that will withstand the friction, weather, temperature changes, and wear and tear associated with its location.

Gas Fills: Energy-efficient windows have two or more panes of glass separated by an air gap to slow heat transfer and reduce noise. Traditionally air or dry nitrogen was used between the panes, but recent models are filled with a low conductance gas like argon or krypton that improves thermal performance.

Energy Rating Value:  A window’s ER rating is a measure of its overall performance, based on three factors: 1) solar heat gains; 2) heat loss through frames, spacers and glass; and 3) air leakage heat loss. A number is established in watts per square metre, which is either positive or negative, depending on heat gain or loss during the heating season. Natural Resources Canada provides an excellent Consumer’s Guide to Buying Energy-Efficient Windows and Doors. You’ll find it here.

One more thing to remember: window installation is as important to energy efficiency as buying high quality windows. Poorly installed windows – even very good ones — will function poorly. Gentek windows are backed by decades of window manufacturing expertise. Pride in our products and craftsmanship are at the heart of our commitment to quality. It’s what makes our windows among the best in the industry and our service second to none. Find out more here.