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Demystifying window lingo

Jun 17, 2024 | Public | 0 comments

One of the biggest decisions that a board of directors will face when owning a condo that is more than 20 years old will be to replace the windows and doors.

Boards choosing to query third party expertise on this matter might be looking to make better informed decisions. Here are some tips to help decipher window lingo.


The ENERGY STAR program, which has been evolving since 1992, is a government initiative from Natural Resources Canada (NRCan) and the U.S. Environmental Protection Agency that helps consumers better differentiate products to reduce energy costs and lower greenhouse gas emissions.

To qualify for ENERGY STAR certification in Canada, window manufacturers must subject their products to third-party testing by NRCan accredited laboratories. An energy rating (ER) system is used to help gauge a window’s ability to prevent heat loss, directly contributing to overall energy savings in homes and buildings. This rigorous evaluation ensures that Canadian consumers can compare the energy efficiency of different windows.

A NRCan report in 2018, Paving the Road to 2030: Market Transformation Road Map for Energy Efficient Equipment in the Building Sector, stated that residential windows can account for up to 35 per cent of heat losses in a home, so widespread adoption of advanced window technology could potentially reduce total home energy use by 9 per cent and lower greenhouse gas emissions by more than 5 megatonnes.

U value

Some window companies might promote the U value, which measures how well the glass of the window prevents heat from escaping the home. The lower the number, the slower the heat loss (better insulating properties) of the glass. The U value is based on the R-value used in construction for insulating walls. You can transform the U-Value (imperial) to R-Value with the simple formula: R-Value = 1 / U-Value.

When comparing U values, make certain to compare apples to apples since some companies will present a U value in the metric system expressed in Watts per square meter Kelvin (W/m2·K) versus the imperial system (US): BTU/ hr·ft2·F.

For example, 1.42 W/m2·K in the metric system equals to 0.25 BTU/hr·ft2·F in the imperial system. Comparing the U value in the same metric or imperial system will give you the opportunity to make the right decision when choosing the glass. The U factor for windows in Canada varies from 0.65 to 1.93 (W/ m2·K). The lower the number, the better.

Solar heat gain

Solar heat gain coefficient (SHGC) is another measurement used for the selection of glass. SHGC measures how much solar heat passes through windows. Higher SHGC aids passive solar heating in cold climates but increases cooling needs in warm climates. It’s rated from 0 (no heat gain) to 1 (all solar radiation is heat gain).

In Canada, it ranges from 0.02 to 0.69. Ask for a SHGC above 0.3 to reduce heating cost in the winter and lower than 0.60 to avoid overheating in the summer. Glass with low SHGC will offer less visual transmittance and be darker inside.

Visible transmittance

A window’s visible transmittance (VT) measures how much light comes through the window. The higher the VT, the more natural light will enter the house. In Canada, the average is 0.55 and above.

Air leakage

Air leakage measures the amount of air that transfers through the window. Air leakage infiltration and exfiltration equal or less than 0.02 (l/S·m2) in metric or 0.3 (U.S./l-P) in imperial is good. Many offshore windows have very poor air leakage, which equates to drafty windows

Energy rating

The most important measurement is the ER since it includes the whole window (glass and casement). The ER value serves as a measure of a window’s overall energy performance, indicating its resistance to heat transfer. A higher ER value signifies greater energy efficiency, with calculations based on factors such as U-value, SHGC and air leakage rate. These factors collectively determine the window’s overall energy efficiency rating.

To reduce confusion, consumers will find that ENERGY STAR-rated windows have a sticker where the metrics are listed. Higher ER numbers correspond to reduced heating energy consumption, leading to lower annual energy bills. They also convey better insulation, which minimizes the need for heating and cooling, while enhancing indoor comfort by reducing drafts and temperature fluctuations.

Maximum energy savings can be found in windows that are rated “Most Efficient Energy Star Certified” (ER of ≥40), which are crafted from microcellular PVC.

Thomas Noël is the director of the condominium division for Nordik Windows and Doors, the largest window and door replacement company in Ontario for the residential sector, including townhouses and condominium complexes four storeys or less. He sits on the Expert Advisory Council for Windows for the Ministry of Natural Resources Canada (NRCan) and advised on the launch of the $2.6 billion Canada Greener Homes Grant. He can be contacted at: 1- 888- 677- 5343 or [email protected]

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