Solar Heat Gain Coefficient (SHGC) is an important factor when buying energy-efficient replacement windows. In this blog, Renewal by Andersen® of Nashville takes an in-depth look at SHGC and how it can benefit your replacement window buying decisions.
The Energy Envelope
To understand the importance of SHGC, we must first discuss how energy efficiency works in a typical residential setting. An energy envelope is an enclosure that consists of the attic, exterior walls, and fenestrations: skylights, entry doors and windows, all of which have different insulative components. For example, exterior walls have fiberglass wool while entry doors have insulated cores.
These components create an enclosure that has minimal thermal transfer, which significantly reduces heat loss during cold days and heat gain during hot days. This results in a reduction in indoor heating and cooling requirements, which, in turn, results in energy savings. Energy-efficient replacement windows are available in popular styles, such as double hung windows.
Unwanted Heat Gain
Conventional insulation, such as the aforementioned foam and fiberglass wool, has proven performance against ambient heat. Combined with proper weatherstripping and a regularly maintained heating and cooling system, the energy envelope should minimize unwanted heat gain.
Windows, however, are another matter. Given that they’re mostly made of glass – a naturally conductive material – insulation has to be approached differently. Traditional windows are equipped with single-pane glass, which allows heat to easily pass through them. A bank of bay windows would defeat a well-insulated exterior wall in terms of preventing thermal transfer. The air conditioning system will need to pump out more cool air to make up for the temperature difference, which leads to costly utility bills.
This is why Renewal by Andersen replacement windows are equipped with double-pane High-Performance™ Low-E4® glass as a standard component. Two glass panels separated by an insulating spacer minimize contact between interior and exterior surfaces, reducing conductivity much like a vacuum flask. When set into an insulated Fibrex® material frame, only a small fraction of heat ever makes it through to the indoor space, which helps improve energy efficiency.
Popular window styles like sliding windows generally have large glass areas, which mean they allow more natural light into your home. It is worth noting that direct sunlight is another source of unwanted heat. What we perceive as visible light is merely a small fraction of sunlight, which also consists of three types of ultraviolet (UV) rays and the source of heat from the sun, infrared rays.
Since sunlight easily passes through clear glass, low-emissivity coatings are needed not to insulate, but to selectively reflect UV and infrared rays. Unlike window tints, low-E coatings do not block visible light nor does it make the windows as reflective as mirrors. Instead, what you get is a lot of natural lighting with none of the unwanted parts.
Solar Heat Gain Coefficient (SHGC)
The National Fenestration Rating Council (NFRC) tests, certifies and labels replacement windows based on the following categories:
Insulation against radiant heat (U-Factor)
The amount of natural light that passes through (Visible Transmittance)
The amount of air that passes through (Air Leakage)
The heat from the sun that passes through (SHGC)
These results are printed on the energy performance label attached to the particular replacement window. SHGC is represented as a numeric value between 0.00 and 1.00; the lower the value, the better it is at resisting solar heat gain. A window company that offers custom windows like Renewal by Andersen lets you design replacement windows that conform with your home’s specific energy requirements.
You may be wondering, if double-pane glass and Low-E coatings provide desirable results and if these are standard features, why bother with SHGH at all? The answer is simple: homes located in areas with much colder climates actually benefit from solar heat gain since indoor heating is used more often within the year.
Renewal by Andersen of Nashville is your leading provider of energy-efficient custom replacement windows. Give us a call at (615) 238-9463, or fill out our contact form. We serve customers in Nashville and Murfreesboro, TN.