Blog > Category > Posted: 2023-Jul-20, Updated: 2023-Nov-29

Energy efficiency - breaking down energy ratings

Energy Rating Example
Navigating window and glass ratings can be perplexing, as higher numbers are preferred in some cases while lower numbers are preferred in others. To assist you, here are some helpful tips.

Energy Star Certification

The Energy Star symbol indicates that a product meets or exceeds high-efficiency standards. Currently, more than 70 product categories can qualify for the symbol and, typically, a certified model is in the top 15 to 30 percent of its class for energy performance.

Every ENERGY STAR® certified window, door and skylight is required to leave the factory with a removable label that shows:

  • its certified performance ratings (U-factor, Energy Rating, etc.)
  • the climate zone(s) for which it is certified
  • a description of the product (type, materials, glazing, etc.)
  • its certification information

Energy Rating (ER)

The Energy Rating (ER) for window products is an evaluative rating made by an authorised neutral organisation. All products are assessed using a strict common procedure. A window’s ER rating is a measure of its overall performance, based on the three factors below:

  • solar heat gain
  • heat loss through frames, spacer and glass
  • air leakage heat loss

Higher is better - the higher the rating, the better the performance.

U-Value also known as U-factor

The terms refer to a measure of the heat gain or loss through glass due to the difference between indoor and outdoor air temperatures. The U-value describes how well a product prevents heat from escaping a home or building. U-value ratings generally fall between 0.2 and 1.2. U-factor is particularly important during the winter heating season.

Lower is better - the lower the U-value, the better the product is at keeping heat inside the home.


The R-value represents the resistance a material has to heat flow. It measures the effectiveness of insulation in stopping heat flow. There is no set rating scale

Higher is better - the higher the R-value, the greater the heat resistance.


The CR-value indicates how well a product resists the formation of condensation (Condensation Resistance). CR is reported on a rating scale of 1 to 100.

Higher is better - the higher the number, the better a product is at resisting condensation.

Visual Transmittance (VT)

Visual transmittance (VT) indicates the amount of light in the visible portion of the spectrum that passes through a glazing material.

Lower is better - the lower the number, the less of the sun’s heat is transmitted through the glass.

Solar Heat Gain Coefficient (SHGC)

The SHGC is a measurement of the heat transmitted and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1.

Lower is better - the lower the coefficient, the less inward heat it transmits or the greater the shading ability of the glazing.

Canadian climate zones
Canadian window, door and skylight labels

Related topics

What are Energy Star energy ratings?

What is a U-factor?

What is the Solar Heat Gain Coefficient?

What is an R-value?

What is visual transmittance?

CDN Energy Star Climate Zones

Need more information?

If you would like to know more about window & door ratings, give us a call, request more information via our contact form, or come visit our showroom, - we’d love to help you find a perfect window or door solution!

Request information | 613-838-2211 | Request a quote