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What Is Solar Heat Gain Coefficient?

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Solar Heat-Gain Coefficient (SHGC) is a rating to indicate how much solar radiation passes through a window, door, or skylight into the building. A lower SHGC rating means less solar heat passes through the window, door, or skylight, and a higher SHGC rating means more solar heat is passing through.

Do you want to know how to select the best windows, doors, or skylights for your house or project? We have collected the information to make understanding Solar Heat-Gain Coefficients easy!

Keep reading to learn how to read SHGC numbers and learn which score fits your climate well. You will also find quick tips for interpreting other types of ratings on windows, doors, and skylights. We will also answer some frequently asked questions.

How do you interpret Solar Heat Gain Coefficients?

Solar Heat Gain Coefficient (SHGC) is a number between 0 and 1 representing how much solar radiation passes through a window, door, or skylight to heat the building. The number is a ratio that compares the maximum and minimum amounts of solar heat that could pass through the window.

  • SHGC ratings closer to 0 mean less solar heat passes through the window or skylight.
  • SHGC ratings closer to 1 mean more solar heat passes through the window or skylight.

Do you want low or high SHGC windows and skylights?

The ideal Solar Heat Gain Coefficient (SHGC) will depend on your climate and heating and cooling needs. We created a chart to help plan the best window, door, and skylight SHGC ratings.

Climate & Heating vs. CoolingIdeal SHGC Range
Cool Climate With Long Heating Period and Minimal Air Conditioning0.30 to 0.60
Climate Where Air Conditioning Is Sometimes UsedLess Than 0.40
Climate Where Air Conditioning Costs Are HighLess Than 0.30

More specific selections are available using a tool from the Efficient Windows Collaborative. This is an unbiased agency that informs and educates consumers.

What Ratings Affect Window Performance?

National Fenestration Rating Council (NFRC) issues ratings to indicate window performance. The four ratings given to windows include U-Factor, Solar Heat Gain Coefficient, Visible Transmittance, and Air Leakage.

The NFRC uses SHGC and U Factor to qualify windows, doors, and skylights as ENERGY STAR ® products. We broke down what the NFRC looks for in its considerations.

ENERGY STAR® Qualifiers

FactorWhat It MeasuresRangeLook For
Solar Heat Gain CoefficientHow Much Solar Radiation Enters the Building0-1Low Numbers
U-FactorHow Much Heat Escapes0.20 to 1.20Low Numbers

Visible Transmittance and Air Leakage are essential to consider but are not used in ENERGY STAR ® qualifications. Since most windows and skylights are planned to maximize natural light, the Visible Transmittance rating is a helpful indicator of performance.

We created this rule-of-thumb chart for these factors.

Other Performance Indicators

FactorWhat It MeasuresRangeLook For
Visible TransmittanceHow Much Natural Light It Allows0-1High Numbers
Air LeakageHow Much Air Enters (Drafts)Less Than or Equal to 0.30Low Numbers

Frequently Asked Questions

What are SHGC and U Value?

SHGC and U Value, or U-Factor, are both ratings to indicate the energy efficiency of windows, doors, and skylights. SHGC is a rating to measure how much solar radiation passes through. U Factor is the rating that indicates how much other heat escapes through the window, door, or skylight.

While SHGC and U Factor are important, they are not the only values that affect window, door, and skylight performance. Air Leakage will inform buyers of much air enters in the form of drafts, and visible transmittance will indicate how much light comes through.

Do you want a high or low SHGC?

The ideal SHGC depends on the climate. For warm or hot climates, a low SHGC is best. For frigid climates, a higher SHGC could help maximize heat from the sun.

SHGC is a ratio that indicates how much solar radiation passes through the window, skylight, or door. 0 represents the least amount possible, and 1 represents the most amount of solar radiation possible. SHGC Ratings will be between 0 and 1.

For most climates in the United States, buyers will want the lowest possible SHGC numbers. This is because the costs to air condition a building in the summer months are higher than the costs to heat buildings in the winter.

Letting in less solar radiation in the summer is more important than using solar radiation to heat the house in the winter.

Which windows let in the most heat?

Windows with high Solar Heat Gain Coefficient (SHGC) ratings let in more heat from the sunlight. SHGC is not the only indication of how much heat a window will allow to enter the building.

SHGC only measures solar radiation, and another factor impacts heat entering the building. The second important factor to consider is Air Leakage. Air Leakage can allow warm outdoor air to enter a building in the form of drafts in hot months.

Is .23 a good SHGC rating?

An SHGC of .23 would qualify a window, skylight, or door for the ENERGY STAR ® label. This means that for most climates in the United States, this is a good SHGC rating.

Ratings range from 0 to 1, so .23 is on the low end of the range. Little solar radiation would enter the building, keeping air conditioning costs down.

Resources

(2022). Energy Performance Ratings for Windows, Doors, and Skylights. Energy Saver. Retrieved November 24, 2022, from https://www.energy.gov/energysaver/energy-performance-ratings-windows-doors-and-skylights

(2022). Solar Heat Gain Coefficient Ratings for Windows. International Association of Home Inspectors. Retrieved November 24, 2022, from https://www.nachi.org/shgc-ratings-windows.htm

(2022). What Does the NFRC Label Tell You? National Fenestration Rating Council. Retrieved November 24, 2022, from https://www.nfrc.org/?gclid=CjwKCAiAyfybBhBKEiwAgtB7flGy8BdcCAgURUG8ISGUCNU-5cR4oaDeiWt0rJxDlTcRTa5ACThjARoC2pIQAvD_BwE

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