|
Insulating Windows
Dear Home Power, I read your
article on insulation basics and found it very
helpful and informative. The thing
you brought up only in passing is the
importance of sealing and proper
ventilation—both equally important
for a healthy, comfortable, efficient
home. The other issue I wanted
to point out is the importance of
insulated shading. It isn’t nearly so
important to have R-30 walls if 75
percent of the wall is glass—even if
you spend extra and get triple-pane,
low-E, krypton gas-filled windows.
This still gives a whole-wall Rvalue
of 10 or so (depending a lot
on particulars). If you got “tight,”
double-paned, low-E, argon gasfilled
windows and added insulated
shades, the whole-wall R-value
could be as high as 20 or more, and
cost a lot less (again, depending on
particulars).
An article on insulated shades
(not curtains) and the amazing
difference in total house comfort
and energy use would be a great
service to your readers. Even here in
Alabama, insulated shades are one
of the most cost-effective ways to
seal up the last big leak—windows.
It helps that my wife and I made
the shades ourselves after reading
some about the technology at the
Humboldt State/CCAT Web site (after
following the link from the Home
Power Web site). The best references
on insulation and smart building I’ve
seen are from ACEEE. You might
make those references available to
interested readers, since this is an
extremely important topic! Thanks—
keep up the great work!
John Morris • Cullman, AL
Dear John, Thanks for your good comments.
You’re absolutely right — finding and
sealing leaks (such as around windows and
doors), and ensuring that your home has
an adequate air exchange rate for good air
quality is very important. In fact, each of
these topics could easily be a stand-alone
article.
With any wall system, the whole-wall
R-value depends on many factors, including
the number of windows installed in the wall,
the construction type and thickness of the
framing members (for example, whether you
use 2 by 4 or 2 by 6 studs), and the spacing
of the studs (which influences the amount
of thermal bridging that occurs). As you
point out, the thermal performance of a wall
that is taken up mostly by windows will
be very different than a wall without any
windows, due to the difference in the thermal
resistance of or heat transmission through
the materials. (Those interested in seeing
how changing these variables influences
whole-wall R-values can check out Oak
Ridge National Laboratory’s interactive
online calculator at: www.ornl.gov/sci/roofs walls/AWT/InteractiveCalculators/rvalueinfo.htm.)
Your suggestion of using draperies
and insulating panels to mitigate heat loss
(and gain) through windows is an excellent
strategy. According to the Department of
Energy’s Office of Energy Efficiency and
Renewable Energy, using conventional
draperies can reduce heat loss from a warm
interior space by up to 10 percent. In
addition to closing all draperies at night,
the EERE also recommends closing all
draperies on windows that don’t receive
sunlight during the day. Hanging draperies
as close to the windows as possible, letting
them fall onto a windowsill or floor, and
sealing them at the sides and center (using
magnetic tape or Velcro) may help reduce
heat loss by up to 25 percent.
Specially designed, insulated shades
are also available through several
distributors. I’m most familiar with
the Warm Window thermal shades
(www.warmcompany.com; also available
from www.cozycurtains.com). These
shades incorporate four layers of insulated
fabric and a magnetic edge strip to secure
the edges of the shades to the window
frame. According to company claims, a
Warm Window shade over a single-pane
window boasts an R-value of 7.69. You
can order custom shades or buy a kit
from the companies listed above. Or, as
mentioned, you can download instructions
for making your own at the Humboldt
State University’s Campus Center
for Appropriate Technology at www.humboldt.edu/~ccat/energyconservation/index.html.
Another strategy is to use insulating
window panels, which can have R-values
ranging from 3.8 to 7, depending on their
thickness. These panels, which typically
consist of a core of rigid foam insulation, are
inexpensive, and easy to make and install.
Their two small drawbacks are that they
block out most, if not all, incoming light (if
you’re using them during the day) and take
up storage space when not in use. Thanks
for reading,
Claire Anderson • Home Power
|
