How do I read all those numbers on the energy label sticker on new windows?

The energy label sticker contains key performance ratings that help you compare window efficiency and understand how they'll perform in Ottawa's climate. These standardized ratings are required on all new windows sold in Canada.

Energy Rating (ER) is the most important number - it's a single score from 0 to 50+ that combines all performance factors. For Ottawa's climate zone, look for an ER of 25 or higher for good performance, with 30+ being excellent. This rating accounts for both heat gain from the sun and heat loss through the glass and frame.

U-Factor measures how well the window prevents heat from escaping - lower numbers are better. In Ottawa, you want a U-factor of 1.22 or lower to qualify for ENERGY STAR certification and potential rebates. Premium triple-pane windows often achieve 0.8 to 1.0 U-factor ratings. This number directly impacts your heating bills during our long winters.

Solar Heat Gain Coefficient (SHGC) shows how much solar energy passes through the window, rated from 0 to 1. For Ottawa, a moderate SHGC around 0.3-0.4 works well - high enough to capture beneficial winter sun, but not so high that you overheat in summer. South-facing windows might benefit from slightly higher SHGC values.

Visible Transmittance (VT) indicates how much natural light comes through, also rated 0 to 1. Higher numbers mean more daylight, which is valuable during Ottawa's shorter winter days. Quality Low-E coatings can maintain good light transmission (0.6+) while still providing excellent insulation.

Air Leakage measures how much air passes through the window when it's closed, with lower numbers being better. Look for ratings of 1.5 or less - this is crucial for Ottawa's windy conditions and temperature extremes.

For help reading those ratings against your own orientation, request a free quote through Ottawa Window Pros and go through the label with the installer.