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Windows, Skylights & Doors Rating: USA, Canada, Australia, Europe

Many windows, skylights and glazed doors bear energy labels, to assist buyers in selecting energy-efficient products. If they do not bear energy rating labels, be cautious or distrust them.

Elements of Windows, Doors and Skylights Energy Rating

The rating labels consider the U-factor and the SHGC (Solar Heat Gain Coefficient). These are the most important elements when selecting a window, a skylight or a door, but the rating label may also include other elements as the Air Leakage rating, the Visible Light Transmittance and the Annual Heating and Cooling factors.

The U-factor
The U-factor describes the rate of non-solar heat loss or gain through a window or skylight. It is expressed in units of Btu/hr-ft2-°F or W/m2-°C. The lower the U-factors the better (it indicates greater resistance to heat flow and better insulating value).

The SHGC factor
The SHGC is a measure of the solar radiation admitted through a window, door or skylight. The SHGC is expressed as a number between 0 and 1. A lower Solar Heat Gain Coefficient means less solar heat and more shading.

An example of a window rating label (an NFRC - National Fenestration Rating Council - label, USA).

The NFRC label includes 5 measures of windows, skylights and glazed doors energy performance. The most important are the U-factor and the SHGC.

The label includes also:

- the Visible Transmittance (VT), a measure of how much visible light comes through a windows, door or skylight. VT is expressed as a number between 0 and 1. An higher VT means more transmitted light.

- The Air Leakage (AL), a measure of how much air passes through a square foot of window/door/skylight area (cfm/sq ft) by infiltration through cracks in the assembly. The lower the AL, the less air will pass.

The Condensation Resistance (CR), a measure of the formation of condensation on the interior surface of a window or skylight. The higher the CR rating, the better that product is at resisting it. CR is expressed as a number between 0 and 100.

Energy Star energy labels

It may be a good indicator that a window, a door or a skylight bears a NFRC or other similar labels. But that doesn’t mean the product is necessarily a qualified one, with a high performance. It just means that the manufacturer has submitted it to an organization that has rated it.

It’s different with the Energy Star label. An Energy Star label means that the window, the door or the skylight is a qualified and advanced one. It means that the product has attained levels that meet the qualification criteria in one or more Climate Zones.

It’s also different with the BFRC Window Energy Rating and other equivalents in the European Union. These labels contain bands from A to G, where A is the most efficient and G the least…

Rating labels and Climate Zones

The U-factor, the SHGC and other energy measures of windows, doors or skylights should be valid for your specific climate zone. A very low SHGC is an excellent indicator in warm or mild climates, but it isn’t very relevant in a very cold climate, where the solar radiation admitted through a window, door or skylight isn’t a bad thing.

That’s why Energy Star or the European BFRC and other rating labels establish criteria and ratings in function of specific climate zones.

For information on Climate Zones, see:
Windows, Doors, Skylights and Climate Zones
Energy star U-factor and SHGC values

USA & Rating

USA Energy Star labels (based on the National Fenestration Rating Council rates) are the big reference for buyers in USA …

Energy Star considers four climate zones for windows and skylights in the United States, each with specific U-factor and SHGC values.

For information about these values in each specific USA Climate Zone, see:
USA Climate zones & Windows, Doors and Skylights

CANADA & Rating

Energy Star labels are the big references in Canada… Canadian Energy Star considers four climate zones for windows and skylights, each with different U-factor and SHGC values.

For more details on Energy Star Label in Canada, and the Canadian climate zones, see:
Canada Climate Zones
Canadian Office Energy Office

EUROPE & Rating

The British Fenestration Rating Council has established a scheme to measure the energy efficiency of window, doors and skylights. Is also has established a system looking like the standard EU energy labels applied to other products.

The BFRC Window Energy Rating contains bands from A to G, where A is the most efficient rating and G the least. Only the most efficient windows carry the Energy Saving Recommended logo.

For more information:
Europe Windows & Doors Labeling
Energy Saving Trust UK
British Fenestration Rating Council

AUSTRALIA & Rating of Windows

Australia has the Window Energy Rating Scheme (WERS) to rank the energy performance of windows in typical housing anywhere in Australia. The scheme tells whether a given window is suitable for the three specific Australian climates considered by WERS.

Rated windows get from 0 to 5 stars for both cooling (summer) and heating (winter).

For more information:
Australia Windows & Doors Labeling
Australian GreenHouse Office