What are window ratings?

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.

R-Value

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.

CR-Value

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.

Resources:
Canadian climate zones
Canadian window, door and skylight labels

Related blog posts