How much energy can I
save by replacing my windows?
The average home can attribute about 25% of the energy required for heating and up to 40%
of the energy required for cooling to windows. Replacing the windows may save a
significant fraction of this amount. But be skeptical of salespeople who tell you that
you'll save 40%-50% of your energy bills. If your heating bill is half of your total
winter energy bill, and you replace the windows with ones that are twice as efficient, you
may save about 6% of your total utility bill, or 13% of your heating bill. Also remember
that every home is different. Energy use varies by the home's climate, size, orientation
to the sun, amount of window area, residents' comfort needs, and many other factors.
important is a low-conductivity frame?
A typical frame can account for about 15%-30% of the heat loss or gain through a window.
In effect, the actual reduction in your energy bills due to a better frame will probably
be small. But the frame can have a large effect on condensation. Replacing an old aluminum
frame with wood, vinyl, fiberglass, or a composite can significantly reduce problems with
How wide should the space between the panes be in a double-glazed window?
The air space between the two panes of glass varies between 1/4 inch and 1 inch thick. The
most effective thickness between the panes of glass is 1/2 inch if it's filled with air or
argon, or 1/4 inch to 3/8 inch if it's filled with krypton.
Are low-e coatings a good solution for reducing cooling bills in summer?
If the window has only the standard low-e coating it will only help a little in the
summer. However, spectrally selective low-e coatings are designed to block much of the
heat from the sun, and reflect interior heat back into the room in winter.
Do low-e coatings change the color of the window glass?
Very slightly. Most people do not notice the color difference. Low-e products are faintly
reflective and have a slight green tint. Look at a sample first to see if you like the
color and visibility through the window.
How can I replace my existing windows without damaging the stucco or siding of my
Many new window products install over the old window frame. A window contractor removes
the existing glass and sash and installs a new window custom-made to the exact size
directly over the existing window frame. This process makes the window opening slightly
smaller, so you should be sure that the finished window size still meets building code
egress requirements. A complete set of windows in a typical home can usually be installed
in a day.
What does it mean when there is condensation between the two panes of glass in a
This indicates that the seal that joins the window together between the panes has an air
leak. The condensation is caused when warm moist air from inside your home enters the
broken seal between the two panes of glass and condenses on the cold inside of the outer
pane of glass. To make matters worse, when the condensation evaporates away, a mineral
film residue is left behind on the glass. This film looks foggy and is difficult to see
through. If the window has argon or krypton gas fill, the gas will leak out, and even if
it's just air inside, the insulating value will be reduced. When the seal fails in this
way, the window must be replaced.
Are the argon or krypton gases in some double paned windows toxic? No. These
inert gases are part of our atmosphere and are not toxic.