Consumer's Guide – To buying Energy-Efficient Windows and Doors

Catalogue No.: M-92-156/2001E
ISBN: 0-662-27162-9

Section 6 –
The Ratings Game

Now that you know something about window technology and how windows perform, you're probably asking yourself, "How can I verify the performance claims of manufacturers? How do I compare different window types, or the different product lines of various manufacturers? How do I decide which window type is best for my situation? Most importantly, how can I be sure I'm getting what I pay for?"

6.1 Certification, Testing and Standards

With the rapid growth in window technology improvements, a number of organizations and industry associations have been trying to sort out performance standards and certification procedures, both for industry and the protection of consumers.

For example, the Canadian General Standards Board (CGSB) has had in place for some time an insulated glass unit (IGU) standard which sets performance limits on the durability of window edge seals (CAN/CGSB 12.8). CGSB also has a standard for sliding doors (CAN/CGSB 82.1).

The Insulating Glass Manufacturers Association of Canada (IGMAC) certification program requires manufacturers to meet quality control standards and the CGSB edge seal standard (CAN/CGSB 12.8). All IGMAC-certified products bear the following information: IGMAC logo, along with a date, the company name and the place of manufacture. This information is normally stamped into the spacer bar between the glazings or etched onto the glass.

CSA International has a voluntary certification program for windows and doors. For further information, you should contact them at (416) 747-4007.

6.2 CSA Standard A440

The Canadian Standards Association (CSA) has established the CSA-A440 standard. It is called an omnibus standard because it applies to windows constructed from diverse materials. It describes how to measure and rate a window's airtightness, watertightness, wind resistance, condensation resistance, forced entry resistance, ease of operation, and other requirements. It also sets out minimum requirements for all components and their materials, from hardware, insect screens or weatherstripping, to finishes, adhesives and thermal performance. In addition, all windows must be designed to allow on-site reglazing.

The CSA-A440 rating is a minimum to start with when purchasing new windows.

Independent testing by accredited laboratories assures each model meets minimum levels of performance in the three categories: airtightness, watertightness and wind resistance. The National Building Code and most provincial building codes now require that windows used in new low-rise residential construction and renovations meet CSA-A440 requirements and have at least an A1, B1 and C1 performance rating (Fig. 31).

Fig. 31

In general, a window can achieve high resistance to air, water and wind only by incorporating tight-fitting corner joints, good seals, proper gaskets and weatherstripping. Look for a window with a minimum A1, B1, C1 rating and a high Energy Rating number (CSA-A440.2; described below). There are also optional parts of this standard against which manufacturers may wish to rate their product, in areas such as condensation resistance, forced entry, etc.

6.3 The Canadian Energy Rating (ER) System

Although CSA-A440 protects the consumer and is the minimum performance standard referenced in most building codes, the bottom line for the energy-conscious consumer is a window's Energy Rating, or ER number, based on the CSA-A440.2 Energy Performance of Windows and Other Fenestration Systems standard, which applies to all windows and sliding glass doors and the CSA-A453.0 which applies to all swinging or entry door systems.

A window's ER rating is a measure of its overall performance, based on three factors: 1) solar heat gains; 2) heat loss through frames, spacer and glass; and 3) air leakage heat loss. A number is established in watts per square metre, which is either positive or negative, depending on heat gain or loss during the heating season. The range is wide. Fig. 32 lists the typical ER ratings for windows most commonly available.

Fig. 32

The ER system is based on a formula which calculates a single ER number for a specified window size in each of seven window categories (e.g., a 600 mm by 1220 mm/24 inch by 48 inch casement selected as representative of that window type). Because all window Energy Ratings (ER) are evaluated in the same way, this makes it easy to do comparison shopping between different manufacturers–although a consumer should be aware that the rating given will be for windows in the standard size, and not a particular window.

However, there are still several things to keep in mind when comparing ER numbers of different windows. As you can see by looking at Fig. 32, most fixed windows tend to have better (higher) ER numbers than operable ones. There are two reasons for this. First, the standard size for a fixed window is nearly twice as large as most of the operable windows and thus has more glass area relative to frame area. Frames are also thinner because they do not need separate moveable sashes. This translates into more solar gains and less frame losses – hence a higher ER number. Second, fixed windows tend to have less air leakage compared to operable ones. There is always going to be less air leakage with a window you can't open than with one you can. This translates into less heat loss and a higher ER number for fixed windows.

It stands to reason from this discussion that, when you shop, make sure you're comparing apples to apples. Compare ER numbers within each window category–fixed, casement, sliders, etc.–because the ER numbers vary considerably for each type.

Although intended only for comparison purposes, the ER number may be a good indicator of the effect windows will have on the annual heating costs in the home. A positive ER number means the windows actually add more heat to the home than they lose during the heating season, decreasing the home's heating costs. An ER number of 0 should be considered a minimum performance level for a fixed window. A window with an ER of zero loses as much heat as it gains over the heating season. Consequently, it will have no impact on the house's annual fuel consumption.

A negative ER means a window loses more energy than it gains, making the heating system work harder. The lower the number, the more heat is lost and the harder the heating system has to work in colder weather. For example, an ER of -38 is worse than an ER of -20. An ER number of -11 is a good minimum performance level for an operable, standard high-performance window.

However, some of the super high-performance windows coming onto the market (for instance, ones with low-profile, foam-filled fibreglass frames, insulated spacers and low-E, gas-filled triple glazing) may provide positive ER numbers, even for operable units.

The ER system is a major step in giving consumers the information they need to make informed decisions about the energy performance of windows. It is a rating solely of a window's performance–regardless of how, or with what materials, it was built.

Just looking at the ER numbers might not be enough information if your house differs from the average house used for the calculations (i.e., if it is heavily air-conditioned because of large internal loads, or has extreme solar gains that come with a passive solar-heated home). How do designers deal with this problem? The answer is the ERS rating system.

6.4 The ERS Rating: Adding Location and Orientation

A window's ERS rating is its ER value calculated for a specific house. It is calculated based on house type, municipal location, window orientation and window size. Although simple ER comparisons are often all that is needed for most houses, the design of an ultra-low energy home (like the Advanced House), a passive solar house, or solar spaces might warrant use of ERS for comparison. By obtaining solar heat gain, rate of heat flow and air leakage characteristics of a particular window from the manufacturer, a more accurate picture of window performance is calculated according to the CSA-A440.2 standard.

The ERS values are used to make comparative estimates of the effect on a home's annual heating energy requirements of installing a particular window in a specific orientation. It allows the designer to compare two seemingly identical windows–by their ER numbers–while ensuring that the right window is selected for the right location and compass orientation.

6.5 Making Ratings Work for You

Energy performance is only one of many considerations in the purchase of a window. Appearance, price and durability are also important considerations. A high-performance window that meets CSA standards and has a good ER number will also tend to be better designed and manufactured, and will offer better resistance to condensation.

High-performance windows, described in the next section, offer other benefits too–better comfort levels, less condensation problems and lower sound transmission. While these benefits are not something you can readily put in the bank, they may be important to consider as you make your decision.

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