Technology Snapshot & Benefits:
Significant economic savings can come from modern
windows. Unless recently upgraded, your windows are likely a major source of
heat loss. In cold climates, windows transfer heating energy out of the
building through both conduction and radiation. Additionally, depending upon how
weather-tight the frame and seals, windows may transfer energy by convection as
well. This situation is reversed in hot climates, with windows allowing heat
into a building and forcing expensive cooling systems to work overtime.
Typical walls in homes are insulated to a level of
R-11 to R-19, yet a single pane of standard glass has an insulating value of
about R-1. In other words, heat can leak out of, or into, a building about 11
to 19 times more easily through glass than through the wall. This is why your
grandparents insisted on installing "storm" windows for the winter in northern
climates - to boost window-insulating value to R-2, or perhaps R-2.5 with a good
seal and tightly trapped air between the panes.
Modern windows using specially developed E-glass are
much more effective at keeping heat and cold where you want them. Most
progressive window manufacturers offer several lines of energy efficient glass
with "R" values in excess of R-4. New designs still in laboratory development
promise R-values of 10 or more.
Since glass is a fixed part of the building
envelope, it performs 24 hours each and every day. With energy efficient glass,
less fuel is required for a given level of comfort with corresponding cost
savings and pollution savings.
Estimated Cost Savings:
Assuming the same or greater level of comfort that
you are used to, you can save a lot of energy and money by eliminating heat loss
or gain through windows. It is common in Northern climates to save 30-40% of
annual heating costs with super-efficient windows. With a monthly heating bill
of $200 dollars, this equates to an estimated savings of $60-80 per month. Some
large homes cost as much as $600 per month to heat, and the savings for these
homes could approach $240 per month.
The value of new windows depends upon how much glass
area you have in your home and upon local climate. The
National Climatic Data Center (NCDC) provides an historical record of departures of average daily temperatures from a
reference temperature of 65 degrees F. This information is available as
"Heating Degree-Days per Year" and provides a very useful estimate of how much
energy can leak through windows.
For new homes, getting efficient glass is simply a
matter of working with a builder or architect to specify performance glass. With older homes, the choice of retrofit is a little more problematic. It is
unlikely that the glass in your house will suddenly "conk out" or reach the end
of its useful life like a failed furnace or hot water heater. Therefore, you
will be faced with the prospect of switching out older intact glass panels for
newer glass panels. Nonetheless, this can improve comfort and lower operating
expenses. Capital costs can be $5,000 to $10,000 or more, and still make sound
economic sense when combined with a program of debt consolidation and/or
Selection of glass may depend on local climates. Windows can be "tuned" by the
manufacturer for southern or northern exposures and for different climates. Be
sure that you get the right glass for you.
Installation (Getting It Done):
In addition to considering new windows throughout, also consider supplementary
performance windows that can be treated as storm windows, in addition
to your existing glass. Particularly if your house has period architecture, this
option allows you to retain the original glazing and sash while enjoying
economic savings and the enhanced comfort of performance windows. Be sure to
get bids from two or three (or more) window manufacturers, installers and/or
glazing contractors to gain immediate perspective on the true costs of windows
and installation in your area.
Videos On This Topic:
From EcoBroker International:
From Other Sources:
How to Save Energy with
Energy Star Windows (1:53) - The Home Depot - Replacing your standard
windows with Energy Star approved windows can help save you up to $465 each
year. Find out more in this short video from The Home Depot.
Energy Efficient Windows (1:25) - HGTV -
Watch this short
clip from HGTV's "What You Get for the Money" to find out the basics of why
energy-efficient windows are a good choice and how they can save you money.
in Windows (1:41) - This Old House -
Tom Silva from
This Old House visits the International Builder's Show in Florida to find out
the new ways companies are making energy-efficient windows not only for
functionality, but for beauty and visual appeal as well.
(1:22) - Better.tv -
In this video,
find out how to properly make use of your blinds to help increase your home�s
energy efficiency and reduce heating and cooling bills.
More Information On This Topic:
U.S. Department of Energy's Building Technologies Program: Windows, Doors, and
Fenestration Rating Council (NFRC): Window Energy Performance Label
Star® Purchasing Tips
Residential Windows, Doors, and Skylights Key Product Criteria