Thermal Replacement Windows
Many homeowners are bombarded with sales
pitches about thermal replacement windows. Because the window
replacement business is generally more profitable than other home
service businesses, there are many companies pushing windows in the
Why Replace Your Windows?
The number one reason people replace their
windows is to realize substantial savings on utility bills. The second
biggest reason is that good quality replacement windows deliver large
savings in maintenance costs.
Many people are simply tired of wrestling with
old windows that are hard to open and close or that won't stay open.
When old windows need scraping, new putty and repainting, it's an ideal
time to consider replacement.
Replacing windows is also an opportunity to
upgrade your home in terms of style and resale value.
New Windows Can Save You Money on Utility
Window salespeople make many claims about
energy savings. How true are these claims? Good quality windows,
installed properly, can yield substantial energy savings. How much you
save depends on the type of window you choose and the type and condition
of the windows you are replacing.
In the average home, 38 percent of the heat
loss is through windows and doors. If your home has drafty single-pane
windows or single-pane aluminum sliders, the heat loss from windows may
be as much as 50 percent. The poorer the performance of your old
windows, the more dramatic the savings and the sooner energy savings
alone will cover the cost of your new window investment.
Many people don't realize that you don't have
to replace your old windows with new ones that have the same opening
Air leakage in and around windows is a big
factor in the window's overall thermal performance. In terms of air
leakage, the best window is fixed; that is, can't open or close. There
simply aren't any gaps and openings for air to find its way through.
While useless for ventilation or for escaping a
fire, fixed windows may be an excellent option in certain locations.
Nearly as good are "casements" or awning-style windows that crank open
and closed. Because the seals are compressed slightly when the window is
closed, it is difficult for air leaks to develop.
The least efficient opening style is sliders.
Many people select sliders simply because that is what they've always
had. There are plenty of good sliders on the market, but they have to
rely more on other features, such as low-E coatings (see below) and more
glazing layers, to deliver top energy performance. Sliders, which have
more joints and gaps, are also more susceptible to air leaks as the
seals age and get worn or lose their resiliency.
The window frame is the key to the long-term
structural integrity of the window. If the frame warps or cracks, the
window's performance can suffer enormously. And, as much heat can be
lost through the frame as through the glazed (glass) portion of the
Both wood and vinyl frames perform well,
whereas a metal frame doesn't often contain heat well. However, metal
frames are generally stronger, which becomes a factor in commercial
applications or with extra-large windows.
For normal residential windows, most homeowners
choose vinyl or wood. With vinyl windows, avoid frames that are held
together with screws because they tend to loosen over time. Instead,
look for "welded" seams, where either heat or chemicals have been used
to fuse the joints.
In terms of energy savings, wood and vinyl are
comparable. Some people prefer the aesthetics of wood, though it lacks
the maintenance-free aspect of vinyl.
Most older windows are made with a single layer
of glass. The most popular replacement windows are made with two panes
of glass. Some people opt for triple-pane windows to maximize the
improvement in thermal performance.
Added glass layers improve performance in two
First, enclosed air and other gases are
effective insulators. The more enclosed spaces the window has, the less
heat can escape. Each layer of glass also provides more surfaces for
low-E coatings. Some windows use a plastic film suspended between two
layers of glass to achieve a triple-pane effect at a lower cost.
Low-E coatings are almost invisible finishes
that are usually applied to glass. While they let through most of the
light humans can see, they block much of the heat-intensive infrared
light, thus improving the window's insulating value. Some windows have
the low-E coating on a film suspended between two layers of glass,
creating the effect of a triple-glazed product.
While plain air is a good insulator, some fill
gases, like argon, krypton and carbon dioxide, are even better. The gas
or combination of gases affects the window's overall thermal
Fortunately, the National Fenestration Rating
Council has developed a rating system that considers nearly all of the
One element the NFRC rating system doesn't
account for, however, is the long-term durability of the product because
it rates the window only when it is new.
The NFRC gives each window a U-factor rating.
The U-factor is the inverse of the more familiar R-factor used in attic
insulation. So a U-factor of .5 equals an R-factor of 2. The lower the
U-factor the better it is.
When comparing windows, check for the NFRC
label and look for the U-factor. The first number after the words
"U-factor" is the rating that's appropriate for residential purposes. It
will be marked "AA" or "Residential."
The U-factor marked "BB" or "Non-Residential"
is for commercial window applications. Use the U-factor rating to make
meaningful comparisons. Be wary of a window vendor who won't provide
Purchasing the Best Window for Your Home
Obviously, you need to get price comparisons to
make a decision. Keep in mind that a good portion of your cost is
installation, so it makes sense to leverage those costs by installing a
better window. Here are some guidelines:
Buy a double-pane window with a low U-factor
- You don't expect to live in the home long.
- You have less expensive gas or oil heat.
- You expect energy prices to remain stable or
- You expect to have more income in 10-15
Buy a triple-pane window with a very low
- You expect to live in the home for 10 years
- You have more expensive electric heat.
- You expect energy prices to rise sharply.
- You expect to have less income in 10-15
The NFRC ratings don't address window
durability directly. If the windows warp, leak or loosen over time,
their U-factor ratings are likely to plummet. Your best resource for
choosing a durable, problem-free window is to rely on the advice of a
reputable installer. He or she will be interested in your long-term
satisfaction and will quickly steer you clear of windows that don't hold
You can also inspect the window before buying.
Look for a good fit between parts. Slip a business card between any
slidable sashes and the frame. The card should slide, but there should
be some resistance.
Low U-factor ratings and durable construction
are both determined by attention to details. In general, the better
rated windows will be better made as well.