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<H1 class=title>Windows That Perform Better Than Walls</H1>
<H3 class=subtitle>If you choose the right glazing, your windows can gather more
energy than they lose</H3>
<DIV class=post_data style="PADDING-TOP: 3px">The common perception that windows
are “energy holes” is a bad rap. Since today’s high-solar-gain triple-glazed
windows gather more heat than they lose, good windows perform better than an
insulated wall. After all, a wall can only lose energy, while windows can gain
energy during the day to balance energy lost at night.</DIV>
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<P><STRONG>The Canadian window-rating system</STRONG><BR>In Canada, windows are
rated according to the ER (Energy Rating) method. For those who live in cold
climates, the Canadian ER system is arguably an easier-to-understand method of
rating windows than any system used in the U.S., where NFRC window labels cause
a fair amount of head-scratching. </P>
<P>As explained on a <A
href="http://oee.nrcan.gc.ca/publications/infosource/pub/renovate/Consumers_Guide_EE_Windows_Section06.cfm">Natural
Resources Canada Web site</A>, “A window’s ER rating is a measure of its
<EM>overall</EM> 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 meter, which is either positive or
negative, depending on heat gain or loss during the heating season.”</P>
<P>While windows with a negative ER are “energy holes,” windows with a positive
ER act like heaters. Poorly designed windows can have ER ratings as low as -25,
while the best-performing triple-glazed windows have an ER of about +1 (for
operable windows) or +8 (for fixed windows). </P>
<P><STRONG>South-facing windows produce the most energy</STRONG><BR>Consider a
1-square-meter fixed window equipped with the best available triple glazing
installed in southern Canada. Over the course of a heating season, this window
will, on average, perform like an 8-watt heater. This level of performance is an
average based on all four orientations; if the window faces south, it will
contribute much more than 8 watts.</P></DIV></DIV></FONT></DIV></BODY></HTML>