Get Energy-Efficient Windows

		Whether in a new house, or retrofitting and older home, windows can make a significant difference in your energy consumption. For most homes in BC, the best windows are ones that will minimize heat loss and maximize solar light gains. It is equally important that windows are installed properly. Affordability Windows are a relatively expensive place to make energy efficient changes. The difference in heat retention between an old window and a new energy efficient window is small, so they are not the most effective place to focus if you have limited resources. However, if you are building a home, buying a home, or renovating, the added cost of windows with increased energy efficiency is definitely a worthwhile investment. If you aren't currently in a position to replace your existing windows, draftproof any gaps around them, add storm windows or coverings, and use blinds or drapes to maximize their efficiency. Cost savings Upgrading to energy efficient windows can cut your annual energy costs by up to 20%. Health & comfort Efficient windows make your home more comfortable all year round by reducing drafts and holding in the heat during winter, and keeping it out in summer. Some energy efficient windows can also reduce UV fading of your furniture and flooring. Environmental considerations Finding windows with a low environmental footprint can be difficult. Many modern windows are framed with vinyl, a plastic that is toxic to manufacture and that will persist in the environment for millennia. Wooden windows can be sourced from a sustainable supplier, but need to be painted regularly. Aluminum frames tend to be less energy efficient as they conduct heat easily. Weigh your options and make the most sustainable decision available to you.

What you need to know

Window Efficiency Definitions

• U-Value – This is the flip side of R-value. Where R-value measures heat retention, U-value is a measure of heat loss, also known as thermal transmittance. Therefore, while you want your insulation to have a high R-factor, you want your windows to have a low U-factor.
• Solar Heat Gain Co-efficient (SHGC) – This is also known as solar factor, or g-value, measures how much a window will absorb heat from sunlight. It is a number between 0 and 1, where a low SHGC means less heat gain.
• Visible Transmittance (T_vis) – is a measure of the amount of visible light that makes it through a window. A reduction is SHGC is likely to be accompanied by a reduction in visible transmittance.
• Air Leakage (L50) – Measures how much air leaks in and out of a window when it is closed.
• Low-e stands for low-emittance coating. These are microscopically thin layers of metal or metallic oxide that are coated onto the window glazing. Different types of coating have different properties, but all are designed to lower heat flow through the window – some reflect heat back into the building and others reflect heat back outside.
• Condensation resistance (CR) – Expressed as a number between 0 and 100, the CR measures how well a window assembly resists the formation of condensation on its interior surfaces.
• Glazing or fenestration – refers to your homes windows, or the amount of your house that is covered in windows.

Energy Efficient Window Construction

• The most common types of window frames are wood, vinyl (PVC), and aluminium.
• Wood frames are energy efficient, but can be expensive to purchase up front and need regular upkeep to protect them from water damage. Aluminium frames are inexpensive but the least energy efficient. Vinyl frames are inexpensive and can be quite efficient.
• Energy efficient windows have two or more panes of glass separated by an air gap to slow heat transfer and provide noise insulation. These are known as double paned or insulated windows. 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 gives even better thermal performance and significantly lowers the U-value.
• 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 and created condensation problems around the window edges.
• New spacer products, also called warm spacer technology, or warm edge spacers, have been developed from materials with a low conductivity rate and high thermal efficiency, such as: fibreglass, vinyl, silicone foam and reinforced thermoplastic.
• In addition to energy efficient window types, the location and size of windows is a key factor in energy efficiency. If you are building or remodelling, locate most of your windows on the south side of your house, and minimize glazing on the north side. With a properly designed overhang, your southern windows can provide winter heat and light, but because of the higher angle of the summer sun, the overhang will shade you from the hot direct rays in summer.
• Locate small windows on the north side of the house for cross ventilation in summer.
• Installation of the windows is as important to the energy efficiency of the home as just getting high quality windows. Poorly installed high quality windows will function poorly.
• Thermal Imaging Assessments using an infrared camera are now available for many BC home and building owners. The resulting images identify where your house in leaking heat or has moisture issues.
• Check in regularly to look for new rebates and savings on windows and other energy efficiency products.
• BC Hydro's Business tips Buying Guide has some more information on windows. When you read the business information bear in mind that while many commercial buildings struggle to keep cool in summer, most residential energy loads are from heating in winter.

FAQ

I have beautiful old six-pane farm windows that I don't want to replace. But I don't want to waste energy either – what can I do?
You can have new windows made in almost any style and size, from sleek and modern to a heritage house design. However, if you don't plan to replace your windows, you can improve their efficiency by having fitted storm windows made for them to attach in winter. Storm windows usually attach to the outside of your windows, although some are made to seal on the inside. In addition, use window coverings such as lined curtains, and seal any gaps or cracks around the window frames.

We only have enough money to either add some insulation in our attic, or replace two large picture windows. Which choice will be more energy efficient?
Almost certainly adding the insulation will give you more bang for your buck than upgrading your windows. A window, any window, is kind of like a hole in the building. Some holes are a little smaller and less leaky, but they are still holes. Upgrading windows is certainly important, but unless you already have more than the recommended R-value of attic insulation for your area, insulation is likely to make more of a difference.