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Fenestration Products –
Energy Performance for ENERGY STAR® Qualification

U-Value

A U-value indicates the rate of heat transfer. The lower the U-value number, the slower it transfers heat from a warm area to a cold area. Equivalent R-Values have been given to help you understand the U-values. An R-Value is the inverse of a U-value and indicates the resistance to heat transfer. The higher the R-Value number, the more insulative the product is. The R-Values given are in imperial units. Neither the U- or R-value account for heat energy from the sun (solar gain).

Solar Heat Gain Coefficient (SHGC)

The solar heat gain coefficient (SHGC) indicates the amount of solar gain through a pane of glass. It ranges from 0 to 100. The higher the number, the better the solar gain.

Energy Rating

The Energy Rating (ER) value is calculated using a formula that balances a product's U-value with its potential solar heat gain coefficient (SHGC) and its airtightness. The higher the number, the more energy efficient the product. The ER scale was recently modified so that all products now have a rating of between 0 and about 50. (Under the previous rating scale, it was possible for a product to have a negative ER number.) The higher the ER number, the better the product's thermal performance.

Airtightness and Other Ratings

All windows and sliding glass doors must be rated for their airtightness, watertightness, wind load strength, resistance to forced entry, insect screen strength (windows only) and ease of operation (sliding glass doors only) when they are installed in new homes or other buildings. Provincial and local building codes require different airtightness, watertightness and wind load strength categories depending on the climatic conditions.

Airtightness Categories – Windows and Sliding Glass Doors
Type Least Airtight Most Airtight
Most operable windows A1 A3
Single-hung windows* A1/Fixed A3/Fixed
Single sliding windows* A1/Fixed A3/Fixed
Non-operable (fixed) casement windows A1 A3
Picture windows Fixed (pass/fail rating)
Sliding glass doors A1 A3

*Operable and non-operable sashes may be tested and rated separately for single-hung and single sliding windows.

Other Categories – Windows
Test Lowest Category Highest Category
Watertightness B1 B7
Wind load strength C1 C5
Insect screen strength* S1 S2
Resistance to forced entry F10 or F1 F20 or F2

*This test measures only how well the screen mesh stays fastened to the screen mesh frame, not how well the insect screen stays fastened to the window frame. Most insect screens are designed to be easily removable from the window to allow for egress in case of an emergency. An S1 rating is normally adequate for residential applications.

Other Categories – Sliding Glass Doors
Test Lowest Category Highest Category
Watertightness B1 B4
Wind load strength C1 C3
Ease of operation E1 E3
Resistance to forced entry F1 F2