Decipher the Ratings: A Guide to Energy Star®

Shopping for windows and doors is easy if you select a product that is Energy Star®-qualified. The products are clearly marked with standardized labels identifying which climate zones they are suited to. Read on to understand what the individual ratings mean and how the Energy Star® program works.

Decipher the Ratings: A Guide to Energy Star®

The basics of energy-star®

Energy Star®-qualified windows, doors and skylights will reduce your home energy costs by 7 to 12 percent. They will also reduce drafts, condensation and noise transfer.

For the program's purposes, Canada is divided into four climate zones based on annual average temperature. Zone A is the mildest zone, while Zone D is the coldest. Energy Star® sets minimum ratings that a product must meet to be qualified in each zone.

When shopping, make sure the window or door is qualified for your zone. For more energy savings, opt for a product that is qualified for a colder zone – many are qualified for more than one zone.

How a product qualifies

There are a number of ways in which the performance of windows and doors can be quantified. It’s a little technical, so we’ll explore them individually. To qualify for the Energy Star® program, we use the Energy Rating (ER) or the U-Factor.

  • U-Factor: U-Factor measures heat transfer. The lower the U-Factor, the slower the transfer of heat from a warm area to a cold area. This is the inverse of an R-value, which is commonly used with other construction materials to measure the insulation value. These values do not account for any heat that is gained from the sun through the window glass.
  • Energy Rating (ER): An energy rating balances a product's U-Factor with its solar heat gain and airtightness. Ranging from 0 to 50, a higher energy rating indicates a more energy-efficient product.
  • Solar Heat Gain Coefficient (SHGC): The solar heat gain coefficient is exactly what it sounds like – a measure of the solar heat gained through a pane of glass. It ranges from 0 to 100, with 100 having the most solar gain.
  • Visible Transmittance (VT): Ranging from 0 to 100, visual transmittance measures the amount of visible light that can pass through the product. A higher value means more light will pass through.
  • Air tightness and other standards: Products are also tested in accordance with standards that measure airtightness, watertightness and strength.