Has the insulated glass in your windows
fogged up? Has it lost its seal? You're
certainly not alone. Insulated glass has been around
since 1945 when PPG Industries first offered its new
glass to the U.S. market. It found limited use
until the late 1970s when energy prices peaked at
historic highs. Then "thermopane" glass as it
was known became a fixture in commercial buildings -
especially in northern climates. Increased
emphasis on energy savings and a slew of tinted and
medium-performance coatings really changed the way
people thought about glass in their houses.
Since the 1990s low-e coatings have been developed
for both northern and southern United States
climates and the resulting energy savings have made
insulated glass a "must" for all new buildings.
Almost all buildings now use insulated glass.
Unfortunately the public was never told that the
insulated glass in their windows would, sooner or
later, fog up due to seal leakage. Companies
in the 1980s offered 20 year and even lifetime
warranties. Unfortunately the seals for
insulated glass do not last that long - except in
the manufacturer's laboratories. These long warranties relied on
lawyer legalese that amounted to very little
coverage or the company expected the customer would
move or lose the warranty paperwork. Even
worse, in a large number of cases, the window
company actually went out of business leaving
customers holding worthless warranties.
also speculate that some "less than honest" window
manufacturers know their insulated glass seals will
break down long before their warranty longer than
the industry average. They use cheaper single seal
insulated glass in their windows. My guess is
that they factored the savings of using cheaper
seals against the expense of supplying replacement
glasses to consumers who are able to prove their
warranty. It's a financial decision that has
no basis in the actual expectation of the life of
their insulated glass but they didn't explain it
that way to consumers. Consequently
consumers did not and do not know that their
insulated glass will need to be replaced long before
the actual window frame has to be replaced.
A better way to think about insulated glass is to
think of it like tires on your car. Eventually
you're going to have to replace them. As a
long-time glass company owner, my experience is that
the dual-seal insulated glass that we install will
last between 10 and 20 years before the seal breaks
down. Our suppliers offer us a 10 year
warranty and we pass that along to our customers.
My own experience is that the payback for insulated
glass in energy savings vs the lower cost of
monolithic window glass (plain old single-strength 3/32" window glass) is about 10 years.
Unfortunately there are so many variables (including
huge variations in the cost and types of windows,
types and thicknesses of insulated glass, labor cost to replace or retrofit,
that there is little in the way of empirical
evidence about actual "payback" for the investment
in insulated glass. In addition to the
higher cost of insulated glass and the saving in energy costs, there is a
comfort level that must be considered. Windows with insulated glass make
the house much more comfortable.