Breaking Down SHGC Ratings For Windows


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Breaking Down SHGC Ratings For Windows

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Explaining SHGC (Solar Heat Gain Coefficient)

The Solar Heat Gain Coefficient (SHGC) rating is an important factor to consider when looking at the energy efficiency of windows. This rating measures how much solar radiation can pass through a window or skylight, and it helps determine how much heat can enter a building through the windows. 

The rating is represented as a ratio, where 1 represents the maximum amount of solar heat allowed through a window, and 0 represents the least amount possible. For example, a window with an SHGC rating of 0.30 allows 30% of the available solar heat to pass through. The rating takes into account the entire window assembly, including the glazing, window frame, and any spacers.

How Is SHGC Measured?

The National Fenestration Rating Council (NFRC) is responsible for testing window products and assigning SHGC ratings. They use a specific formula to calculate the SHGC rating, which involves multiplying the shading coefficient (SC) by 0.87. The shading coefficient is a metric that determines the thermal performance of a glass unit.

To find the shading coefficient, the NFRC compares the solar gain passing through a glass unit to the solar energy passing through 3mm clear float glass. The lower the shading coefficient, the better the window’s SHGC rating.

What Is a Good SHGC Rating?

The ideal SHGC rating for a window depends on the climate of the region where the window will be installed. In heating-dominated climates, where extra warmth from sunlight is beneficial, windows with a higher SHGC rating (between 0.30 and 0.60) are recommended. These windows allow more solar heat to pass through, helping to warm the house during the winter months.

In cooling-dominated climates, where the main concern is keeping the interior cool, windows with a lower SHGC rating (less than 0.40) should be used. These windows block more solar heat from entering the building, reducing the need for excessive air conditioning.

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For regions with mixed climates, where both heating and cooling are required, a balance needs to be struck. Windows with an SHGC rating of less than 0.40 are generally recommended, but the specific rating depends on the relative importance of heating and cooling in that region. 

For example, the Northern region requires a relative u-factor between 0.22-0.26  and a relative SHGC between, 0.17-0.50 while the Central region requires a u-factor of 0.24-0.28 and an SHGC of 0.4 or 0.23 depending on the specific region. The Southern region has the highest maximum u-factor requirement of 0.32 and the highest an SHGC requirement of 0.23.

Benefits of a Low SHGC

Opting for windows with a low SHGC rating offers several benefits. First and foremost, low SHGC windows help keep the interior of a building cooler by blocking a significant amount of solar heat. This can lead to reduced reliance on air conditioning, lower energy bills, and increased comfort for occupants.

Additionally, low SHGC windows provide protection against harmful ultraviolet (UV) rays. UV rays can cause fading and damage to floors, walls, and furniture over time. By blocking a larger portion of UV rays, low SHGC windows help preserve the integrity and longevity of interior surfaces and furnishings.

How Can SHGC Be Reduced?

There are several ways to reduce the SHGC of windows and improve their energy efficiency. Manufacturers have introduced various treatments and technologies to influence the SHGC rating of window panes.

  • Tinted and reflective glass: These types of glass have been used for some time, particularly in commercial and office buildings. They reduce the amount of solar heat transmitted through the windows.
  • Spectrally selective glass: This type of glass utilizes tints, coatings, and low-emittance coatings to selectively filter out specific wavelengths of light. By controlling the transmission of solar radiation, spectrally selective glass can achieve desired SHGC ratings.
  • Window orientation and shading: Proper window orientation and the use of external shading devices, such as awnings or overhangs, can help reduce solar heat gain. These strategies limit the amount of direct sunlight that enters the building, thus lowering the SHGC.
  • Window films: Installing window films can also help reduce the SHGC of windows. These films are designed to reflect a portion of the solar radiation away from the window, reducing heat gain.

It is important to note that while reducing the SHGC can improve energy efficiency and reduce cooling costs, it may also impact the amount of solar heat gained during colder months. Therefore, careful consideration of the climate and specific needs of the building is necessary when selecting windows with a lower SHGC rating.

Contact Vistaza

If you’re looking for energy-efficient windows with a specific SHGC rating, Vistaza is here to help. Our team of experts can assist you in finding the perfect windows for your home or commercial building. Contact us today for a consultation and let us guide you towards energy savings and comfort.

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