From Dan on October 2nd, 2009 in CalFinder News, Window Replacement
The most energy efficient windows are concrete walls. They make for terrible views and fire escapes though, unless you’re the Kool-Aid Guy. But seriously, energy efficient windows are really in right now. Every top window manufacturer makes Energy Star-rated windows, the federal government is offering a $1,500 tax credit for your upgrade, energy bills keep on rising and drafty windows won’t stop leaking.
Even better, you can find out exactly how much new windows will cost you by clicking here. Pricing typically varies by area, but federal rebates are nationwide.
If you want to seal up your house so tight that winter drafts will screech and run away in terror, you’ll want the most energy efficient windows money can buy. That window will be an amalgamation of several energy efficient technologies. The most energy efficient windows will have all of the attributes listed below:
Wood, vinyl and fiberglass window frames are all fairly efficient frame types. Aluminum frames are cheaper but very inefficient. However, fiberglass and vinyl have one advantage over wood. Their air cavities can be filled with insulation to provide the absolute highest window frame efficiency available today.
Okay, so the most energy efficient window will have an insulated fiberglass or vinyl frame. Next…
The most inefficient windows have clear single-pane glass. Double-pane windows are fast becoming the standard in efficient upgrades, typically with a low-e coating. But the most efficient windows in use today are triple-glazed, with three panes of glass each separated by a pocket of sealed-in air or gas.
So now, we have an insulated fiberglass window frame with triple-pane glass.
Argon, Low-E Coating and Spacers
Clear glass alone just doesn’t cut it. A low emissivity (low-e) coating should be applied to the glass to control heat transfer in either direction. Low-e coatings reduce energy loss by as much as 50%. Because the window is triple-paned, the manufacturer will apply a soft low-e coating between two panes of glass. Soft low-e coatings are slightly less durable when exposed to air than hard coatings, but are more energy efficient and will not degrade if installed between glass panes.
That space between panes can also be filled with Krypton gas instead of air. Krypton and its more commonly used cousin, Argon, are inert gases, which are more resistant to heat flow than air. Argon is more common because it is much cheaper than Krypton. Krypton, however, can take down Superman and has a better thermal performance, so it will be the gas of choice in the most energy efficient windows.
The best windows also have thermally-improved or low-conductance spacers between the glass panes at the edges of the window. These spacers are necessary in any insulated glass (multi-pane) window. Low-conductance spacers are part of Warm-Edge Technology (WET), which basically just means that they’re made from materials with low thermal conductivity rather than the traditional metal.
Type of Window
How the window operates also affects energy efficiency. Certain types of windows have different air leakage rates. Fixed windows with panes that do not open obviously have the lowest air leakage rates, but are not very practical for ventilation or fire escape.
Single- and double-hung windows, as well as sliding windows, have higher air leakage rates. Awning, casement and hopper windows tend to have lower air leakage rates because unlike their sliding counterparts, their sashes are hinged, providing a better air seal.
Poor installation can also cause wind and water damage to the siding, trim, and inside the house, all of which will affect the energy efficiency of the home in general. So be sure to have your energy efficient windows installed by a pre-approved window contractor.