Why High Energy Efficiency Windows & Doors?

If you are interested in saving energy consider installing high-performance units. Nearly 15-20% of all home energy is lost via windows and doors.  Having energy efficient windows in your home should be a priority.

An informed decision concerning one of the most critical areas of energy loss (or conservation) in your home is paramount.  Here are some useful terms to understand….

INSULATED GLASS: (IG)

Two or more individual panes of glass separated by a specified spacer bar system and then sealed to be air and water tight. The "captured" airspace between the panes of glass forms the insulating barrier. The majority of modern energy efficient window systems utilize some type of insulated glass (IG) application.

EMISSIVITY:

Emissivity is the capability of a surface to emit heat radiation. A black surface is often used as a constant in measuring other surfaces against it.

For example, in measuring the emissivity of a particular IG unit, the IG unit is placed next to a solid black surface and subjected to an identical heat source. Measurements of heat radiated from each surface are then taken. The lower the number results in better heat-reflecting capability.

With relation to energy efficient window systems, lower emissivities are desired.

R-VALUE:

The R-value represents the resistance a material has to heat flow. R-Value measures the insulation properties of a material. The higher the R-value, the greater the resistance. Insulated glass provides a pocket of air to enhance its R-Value.

U-VALUE:

The U-Value is an insulation rating for transparent objects like glass. The term U-value is measured by the amount of heat that escapes a surface, like a wall, ceiling, or in our case, a window. The lower the U-Value, the better the insulation.

The energy efficiency of windows is measured by U-values. Windows, made of glass, are not insulators so they can't be measured in “R-Values.” But since windows obviously have insulating properties, there needs to be a measurement that allows comparison of the types, style and materials of windows.

There is a direct reciprocal relationship between R-values and U-values. To find a U-value, we divide the number ‘1’ by the R-value.

So in other words - the higher the R-value, the better the surfaces are insulated. The lower the U-value, the better a window does it's job of keeping out heat and cold.

SOLAR HEAT GAIN COEFFICIENT: (SHGC)

Solar Heat Gain Coefficient (SHGC) is a measure of a window's ability to reduce heat gain during direct radiation exposure; such as during the summer months in warmer climates. A lower SHGC translates into less direct heat being pulled into the home resulting in lower cooling costs. SHGC and U-value are closely linked since the lowering of one directly affects the other.

LOW EMISSIVITY: (LO-E)

Lo-E refers to the ability of an IG unit to suppress direct heat radiation and absorb indirect heat radiation. By placing a Lo-E coating, which usually consists of a microscopically thin layer of metallic oxides (primarily silver), on a glass surface, the ability to transfer heat radiation is lowered. The heat remains on the side of glass where it originated.

In a nutshell, Lo-E coatings reflect direct heat radiation and absorb indirect heat radiation.

HOW DOES LO-E WORK?

Lo-E glass works based on the angle of direct solar radiation.

Due to the sun's differing angles at various times of the year, Lo-E coatings work well in all seasons. In summer, when the angle is more direct, or "a high sky" they reflect heat. In winter, when the sun's angle is less direct, "a lower sky" they absorb the indirect heat.

GLASS SURFACES:

All energy efficient windows with insulated glass are broken down into 4 surfaces:

Surface 1 (S1): The exterior surface of the exterior pane of glass.

Surface 2 (S2): The interior surface of the exterior pane of glass.

Surface 3 (S3): The exterior surface of the interior pane of glass.

Surface 4 (S4): The interior surface of the interior pane of glass.

These designations are important because the optimum effectiveness of the Lo-E coating is determined by which surface it is applied to.

With Lo-E applications, the heat radiation remains on the side of glass where it originated.

For warmer climates, Lo-E coatings are sometimes applied on S3 and a secondary tint applied to S2 to reduce the initial heat radiation.

Such applications don't work as well in cooler climates since you want some of the initial heat to absorb in order to remain trapped once it tries to leave.  Therefore, the ideal surface for a Lo-E coating in cooler climates is S2.  

Where do I get Super Efficient Windows?