You know you need to purchase windows but do you know how to choose windows to fit your home and life-style? Window shopping is easy when you know what to look for. Just take your time and assess your needs. Windows and doors are offered in an array of styles, shapes and features. First consider which style is inviting to your home and your family. Second, consider what thermal performance features will be ideal for your climate. And thirdly, consider which glass options will be most appropriate by accessing the sunset and sunrise with the location of the windows.? It’s truly that simple. If you want to get more detailed with features such as grids, prisms, or particular hardware and need assistance, simply ask The Design Center at Accent Window.

The Department of Energy (DOE) and the Environmental Protection Agency (EPA) have developed an ENERGY STAR? designation for a host of products, including windows and doors, that meet certain energy performance criteria. Learn more energy saving tips at www.energystar.gov.

What Ratings Should You Look For in an Energy Efficient Window?

U-Value

While shopping for windows, most likely you will find an energy efficient label with the term U-value on it.  In a typical insulated window you have the two panes of glass, the space between the glass, the frame material and usually weather-stripping or sealant that hold it all together.   U-values rate how much heat is conducted through this entire unit – or how much heat is allowed to pass through it. The "U-Factor" is a measure of the rate of heat loss through a window. The lower the "U-Factor", the lower the amount of heat loss. This is important in colder climates, where installing windows with lower "U-Factors" will reduce the percentage of heat that leaves your house.

R-Value

A more familiar term for rating a window’s energy efficiency is R-value. R-values are used to rate how well a material such as insulation resists the flow of heat through it.   A window with a high R-value means it will resist heat loss more and therefore be more energy efficient.  Simply put, the "R-Value" is the inverse to the "U-Factor".

"Energy Star" label which was developed by the U.S. Department of Energy and the Environmental Protection Agency for products meeting certain energy performance criteria. Since the energy efficiency performance of windows can vary due to climate, three different climate zones are designated:

1. Mostly Heating Zone
2. Mixed Heating and Cooling Zone
3. Mostly Cooling Zone

The National Fenestration Rating Council (NFRC)
is a non-profit, public/private organization created by the Window, Door and Skylight Industry. The NFRC has developed a Window Energy Ratings System based on product performance. NFRC labels on window units give ratings for "U-Factor", "Solar Heat Gain", "Visible Light Transmittance" and "Air Leakage".

Types of Materials Used

Window frames are available in a variety of materials including aluminum, wood, vinyl, composite materials and fiberglass. Frames may be primarily composed of one material, or they may be a combination of different materials such as wood and vinyl. Each frame material has its advantages and disadvantages.

Aluminum
This material is in many ways, the best possible way to build a custom window. It is easily shaped and can be bent into a number of different forms. However, it does not insulate quite as well as other materials, since it has a low R-value. Condensation is also a factor, as it can accumulate on the inside of an aluminum window frame. Thermal breaks are vinyl strips that are put inside the frame and can help with insulation.

Wood
Wood is one of the best insulators, with a generally high R-value. Temperature extremes will not cause significant changes in the heat allowed in or out. Condensation is very rare on wood window frames. Wood frames are, however, more expensive. The are also prey to warping, paint peeling, and cracking. They require a significant amount of regular and yearly care.

Vinyl
Vinyl is a shorthand term for Polyvinyl Chloride (PVC) and is one of the best all-around materials that you can use to build windows with. Vinyl is easy to form in many different shapes and can mimic many styles, colors and forms. Vinyl windows are excellent insulators and require little to no maintenance.

Fiberglass
This type of window is relatively new and as such, is not as common as wood or aluminium. Fiberglass windows are best overall insulators, with significantly high R-values. They do not deform, swell, decay, or warp. They can also be colored many ways and are strong enough to tolerate a larger weight of glass.

Glass for Windows

Single-pane. This has very little insulating value with (approximately r-1). It provides only a thin barrier to the outside and can account for considerable heat loss and gain.
Double-pane. To improve a window's energy efficiency the number of glass panes in the unit is doubled, because multiple layers of glass increase the window's ability to resist heat flow.

Types of Glass

Clear glass has been the primary material available for window panes in homes. However, in recent years, the market for glazing--or cutting and fitting window panes into frames--has changed significantly. Now several types of special glazing's are available that can help control heat loss and condensation.
Low-emissivity (low-e) glass. This has a special surface coating to reduce heat transfer back through the window. These coatings reflect from 40% to 70% of the heat that is normally transmitted through clear glass, while allowing the full amount of light to pass through.
Heat-absorbing glass. This contains special tints that allow it to absorb as much as 45% of the incoming solar energy, reducing heat gain. Some of the absorbed heat, however, passes through the window by conduction and re-radiation.
Reflective glass. This has been coated with a reflective film and is useful in controlling solar heat gain during the summer. It also reduces the passage of light all year long, and, like heat-absorbing glass, it reduces solar transmittance.

Glossary of Window Terms

Air Chambers - Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window.

Air Infiltration - The amount of air that passes between a window sash and frame. In windows it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pass through.

Argon Gas - An odorless, colorless, tasteless, non-toxic gas which is six times denser than air. It is used to replace air between the glass panes to reduce temperature transfer.

Awning Window - A top-hinged window that swings outward for ventilation.

Balance System - Device for holding vertically sliding sash in any desired position through the use of a spring or weight to counterbalance the weight of the sash.

Condensation Resistance Factor - A measure of the effectiveness of a window or glazing system to reduce the potential for condensation. The higher the condensation resistance factor, the more efficient the window and glazing system.

Convection - Heat transfer by currents that flow from a warm surface to a colder one.

Double-strength Glass - Glass with a thickness of approximately 1/8".

ENERGY STAR ® - ENERGY STAR ® is an independent U.S. government program establishing a standard set of guidelines to recognize the energy efficiency of various products. ENERGY STAR ® guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, ENERGY STAR ® guidelines have helped double the efficiency of windows they endorse.

Glazing - The process of sealing the glass to the sash.

Grids - Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller lites of glass.

Head - The horizontal top portion of the main frame.

I.G. Unit (Insulating Glass Unit) - Two or more lites of glass separated by a spacer and hermetically sealed at the glass edges.

Jamb - Vertical sections of the main frame.

Lift Handle - A handhold for raising and lowering the sash. Handle implies that the handhold is not continuous across the sash.

Lift Rail - A handhold for raising and lowering the sash. Rail implies that the handhold is continuous across the sash.

Lite - A unit of glass in a window.

Low E (Emissivity) Glass - Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through but reflects long-wave infrared energy which improves the U-value.

Main Frame - The head, sill and jambs sections of a window.

Mullion - A vertical or horizontal connecting unit between two or more windows.

Obscure Glass - Glass that has been made translucent instead of transparent.

Picture Window - A window that has no moveable sash.

R-value - Resistance a material has to heat flow. The higher the R-value, the greater the resistance, the better the insulation. R-values are the reciprocal of U-values (R-value of 4 is equal to U-value of 0.25)

Radiation - Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is either transmitted, absorbed, reflected or a combination of all three.

Sash - The part of the window which contains the glass.

Shading Coefficient - The ratio of solar heat that is transferred through a glazing material relative to the solar heat transferred through 1/8" clear glass. The lower the number the more efficient the window is at reducing solar heat gains.

Sill - The horizontal, bottom section of the main frame.

Slider Window - A window in which the sash move horizontally. Sliders are available in a 2- or 3-lite configuration, with the 3-lite having operable end vents.

Solar Heat Gain - The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.

Spacer - Material placed between two or more pieces of glass in order to maintain a uniform width between the glass, and prevent sealant distortion.

Stile - The vertical sections of the sash.

Tempered Glass - Glass with a surface compression of not less than 10,000 psi, or an edge compression of not less than 9,700 psi. When broken, the glass breaks into pebbles instead of shards.

Tilt Latch - Mechanism that unlocks the sash and allows it to tilt in from the main frame.

Total Unit U- and R-values - The U- and R-values of the window calculated from the average U and R-values from the center of glass, edge of glass, and frame.

U-value - Amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality. U-values are the reciprocal of R-values. (U-value of 0.25 is equal to R-value of 4)