energy efficient window
Windows bring light, warmth, and beauty into buildings and give
a feeling of openness and space to living areas. They can also be
major sources of heat loss in the winter and heat gain in the summer.
In 1990 alone, the energy used to offset unwanted heat losses and
gains through windows in residential and commercial buildings cost
the United States $20 billion (one-fourth of all the energy used
for space heating and cooling). However, when properly selected
and installed, windows can help minimize a home's heating, cooling,
and lighting costs. This publication describes one optionenergy-efficient
windowsavailable for reducing a home's heating and cooling
energy requirements.
Controlling Air Leaks
When air leaks around windows, energy is wasted. Energy is also
transferred through the centers, edges, and frames of windows. Eliminating
or reducing these paths of heat flow can greatly improve the energy
efficiency of windows and, ultimately, of homes. Several options
are available to reduce air leaks around windows; the least expensive
options are caulking and weatherstripping, followed by replacing
window frames.
Caulking and Weatherstripping
Caulks are airtight compounds (usually latex or silicone) that
fill cracks and holes. Before applying new caulk, old caulk or paint
residue remaining around a window should be removed using a putty
knife, stiff brush, or special solvent. After old caulk is removed,
new caulk can then be applied to all joints in the window frame
and the joint between the frame and the wall. The best time to apply
caulk is during dry weather when the outdoor temperature is above
45° Fahrenheit (7.2° Celsius). Low humidity is important
during application to prevent cracks from swelling with moisture.
Warm temperatures are also necessary so the caulk will set properly
and adhere to the surface.
Weatherstripping is a narrow piece of metal, vinyl, rubber, felt,
or foam that seals the contact area between the fixed and movable
sections of a window joint. It should be applied between the sash
and the frame, but should not interfere with the operation of the
window. For more information, see Weatherize Your HomeCaulk
and Weather Strip.
Replacing Window Frames
The type and quality of the window frame usually affect a window's
air infiltration and heat loss characteristics. Many window frames
are availableall with varying degrees of energy efficiency.
Some of the more common window frames are fixed-pane, casement,
double- and single-hung, horizontal sliding, hopper, and awning.
When properly installed, fixed-pane windows are airtight and inexpensive
and can be custom designed for a wide variety of applications. But,
because they cannot be opened, fixed-pane windows are unsuitable
in places where ventilation is required.
Casement, awning, and hopper windows with compression seals are
moderately airtight and provide good ventilation when opened. Casement
windows open sideways with hand cranks. Awning windows are similar
to casement windows except that their hinges are located at the
tops of the windows instead of at the sides. Hopper windows are
inverted versions of awning windows with their hinges located at
the bottom. Windows with compression seals allow about half as much
air leakage as double-hung and horizontal sliding windows with sliding
seals. These would be considered as energy efficient windows. Click
here for more information.
Double-hung windows have top and bottom sashes (the sliding sections
of the window) and can be opened by pulling up the lower sashes
or pulling down the upper sash. Although they are among the most
popular type of window, double-hung windows can be inefficient because
they are often leaky. Single-hung windows are somewhat better because
only one sash moves. Horizontal sliding windows are like double-hung
windows except that the sashes are located on the left and right
edges rather than on the tops and bottoms. Horizontal sliding windows
open on the side and are especially suitable for spaces that require
a long, narrow view. These windows, however, usually provide minimal
ventilation and, like double-hung windows, can be quite leaky.
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