ENERGY STAR THERMAL WINDOWS
Basics
If your home or business was built before the early 1980's and has never been upgraded, chances are the windows and sliding glass doors that were installed are metal-framed single-pane models that are very inefficient compared to today's standards. You may not realize it but as much as 25% to your utility bills are literally going out the window due to this inefficiency. We can help! We proudly sell and install locally-manufactured, Majestic premium Energy Star replacement vinyl windows and doors. They are manufactured locally and superior to almost every other window upgrade at a great savings over most window companies. Contact us for details.
Save money and energy. Installing ENERGY STAR-qualified windows lowers energy bills and saves you money over single-paned and even new double-paned, clear-glass windows.
More than just dollar savings. ENERGY STAR-qualified windows protect from the winter cold and summer sun, while also reducing condensation and interior fading.
What makes a window, door, or skylight energy efficient? Thanks to a host of new technologies, ENERGY STAR-qualified windows, doors, and skylights keep your home cooler in the summer and warmer in the winter, making you more comfortable and saving you money.
Purchasing tips to help you buy with confidence. Every ENERGY STAR-qualified window, door, and skylight is independently certified to perform at levels that meet or exceed strict energy efficiency guidelines set by the U.S. Department of Energy.
Energy-saving tips. Proper installation, orientation, tree planting, and home sealing can help you save even more energy and money!
Rebates. Because installing Energy Star-qualified windows will save energy, they qualify for the 2009 federal tax credit. So you can deduct 30% of the total installed price of the windows just like a PV Solar System.
For over a generation, window manufacturers have been on a quest to improve energy efficiency. Windows represent large insulation voids in a house, and while much heat often moves through the roof and via air leakage at sash seals and trim, expanses of glass can be a significant path. Because the high-tech mechanics and materials behind these improvements can be radically different than the design and construction of traditional windows, understanding the options that manufacturers offer, and what their impact can be on an old house, can help guide anyone considering new windows for historically appropriate replacements or additions.
The Problem with Windows
In simple terms, energy is able to flow through a basic window in two forms: solar radiant heat gain (solar radiation admitted through a window and released indoors), and heat conduction through the materials (frame, glass, etc.). Sometimes this flow is useful, as when sunlight warms a room on a winter day, but when it's going in the wrong direction, its a problem. In regions with high heating bills, windows that allow indoor warmth to be lost to the outdoors are considered to be low in energy efficiency. In warm regions the reverse situation is the the concern: keeping the heat out, rather than in, and limiting cooling bills. Even more important in some ways is the perception of heat or cold by the occupants. In a room that is heated to a comfortable 70 degrees, the inside surface of a single-pane window can be as much as 20 degrees colder, and this can make a person feel cold because the window is not reflecting back their own body heat. A cold window is also prone to moisture condensation, which is unsightly and damages finishes. How then to increase window performance? Typically, by looking for thermal improvements in the three areas of glass, gas, and frames.
Tintings and Coatings
In the search for performance, one of the first places manufacturers looked for improvements was the glass itself. Tinting glass by coloring it with mineral admixtures reduces the percentage of radiation that it can pass. However, because tinting also reduces visual transmittance (the visible light transmitted through the glass), and the coloring looks subtly unlike traditional glass, it became less popular for residential windows than other applications. So manufacturers shifted their attention to another front: altering the surface of the glass. In the past, these alterations have been in the form of reflective coatings and films that limit heat gain and glare, but since the mid-1990s the trend in residential windows has been toward low-e (low emittance) coatings that improve window performance during both heating and cooling seasons.
Low-e coatings are layers of metal or metallic oxides that are extremely thin (on a molecular level), virtually invisible, and permanently bonded to the glass surface. In double-glazed windows, these coatings face into the gap between the panes of glass and are designed to suppress the heat flow through the window. That is the radiation from a warm pane of glass to an adjacent cooler pane. Low-e coatings can also be produced to obtain different levels of solar heat gain. Low solar gain coatings, for example, are preferred in regions where keeping the house cool is the main issue. High or moderate solar gain coatings may be desirable where the emphasis is on heating the house, rather than cooling, and the extra warmth from solar gain is welcome in winter. Luckily for old-house lovers, a byproduct of standard low-e coatings (as well as plain glass) is reducing some of the UV rays that cause fading and fabric damage in furnishings. Plus, these coatings can also be designed to be spectrally selective and keep UV transmittance as low as 16 percent. Even better, low-e coatings are relatively inexpensive options to add to a window ($1 to $1.75 per square foot), a cost that may be nearly inconsequential on high-end windows.
Glass and Gas
Another approach is to enhance the construction of the window, and employing multiple layers of glass is the obvious method. Though the most common configuration for American houses is the double-glazed window. This is two thicknesses of glass separated by an air space that reduces heat and sound transfer. Triple-glazed windows are available for commercial applications or super-insulated houses in cold regions like the mountains. In fact, some manufacturers have developed ways of achieving some of the benefits of triple-glazing without the weight or thickness of more glass by incorporating one or more stretched plastic films between double-glazing.
Today, many manufacturers also do their best to bolster the thermal performance by filling the void with a low thermal-conductance gas. When a multi-glazed window is made using normal air alone, the air space is carefully dried and sealed to guard against condensation and to maximize the insulating ability. Even so, sometimes it can travel in currents that conduct heat between indoors and outdoors. Swapping air for a gas that is more viscous or less conductive helps mitigate this problem. Argon, an inert, nontoxic gas, is commonly used because it's inexpensive and works best in the same spacing as air, about 1/2" between panes. Krypton is a more expensive gas, but it has better thermal performance than argon, so krypton is often the choice for filling windows that must be kept thin (say 1/4" between glazings), which is often the case when trying to maintain the look of historic windows. Mixtures of argon and krypton are also employed to balance cost and performance.
The materials that wrap glass and gas influence window performance too. In the 1960's and 1970's manufacturers started using aluminum spacers at the perimeter of the glass to separate the panes at the proper gap. This was ideal structurally, but a problem arose, as it turned out, thermally. Aluminum is an excellent conductor of heat, and these spacers became an easy path for heat to bypass the glass-and-gas sandwich, compromising the insulating performance of the window and creating cold edges and condensation.
Since then manufacturers have devised a variety of low-conductance edge systems that cut heat loss. Moving to less-conductive metals, such as stainless steel, is one popular approach. This is often used in combination with thermal breaks, clever cross-sectional designs that make it harder for heat to migrate across the spacer. Some manufacturers eliminate metal altogether in favor of materials with better thermal resistance, such as thermoplastics, vinyls, fiberglass, or silicone foam. There are even hybrids that combine a metal or plastic spacer with a desiccant, for instance, or add a thin aluminum or stainless shim to a plastic spacer.
Lastly, glass and spacers have to be held in some sort of frame, and this window component can be a major thermal conductor too. Aluminum frames, for example, are very conductive and can affect energy bills as well as draw condensation. Fortunately for old-house owners, wood is a good insulator and can deliver about the same thermal performance as materials such as vinyl, fiberglass, or composites that are employed for energy-efficient widows today. Plus, wood is light and easily maintained, and has a proven track record of weather service and beauty that man-made materials have several centuries to meet.
Remember, we can help! We proudly sell and install locally-manufactured, Majestic premium Energy Star replacement vinyl windows and doors. They are manufactured locally and superior to almost every other window upgrade at a great savings over most window companies. Contact us for details.