The Solar Heat Gain Coefficient (SHGC) measures the amount of solar radiation admitted through a window, expressed as a number between 0 and 1, where lower values indicate less solar heat gain and better energy performance for most Canadian climates. Understanding SHGC is essential for selecting the right windows to reduce heating and cooling costs whilst improving home comfort throughout Ontario’s diverse seasons.
What Is Solar Heat Gain Coefficient?
The heat gain coefficient SHGC represents how much solar energy passes through your entire window assembly. This performance rating accounts for both direct sunlight transmission and heat absorbed and subsequently released by the glass and frame materials. When solar radiation hits your windows, some energy passes straight through as visible light, whilst other portions are absorbed by the glazing and later released as heat into your home.
The National Fenestration Rating Council (NFRC) provides standardised testing to determine accurate SHGC ratings for all window products. These measurements help homeowners make informed decisions about energy efficient windows that suit their specific climate needs.
What is the formula for solar heat gain?
The most widely used formula for calculating solar heat gain through windows is:
Solar Heat Gain (Q)=SHGC×Window Area×Solar RadiationSolar Heat Gain (Q)=SHGC×Window Area×Solar Radiation
Where:
- SHGC = Solar Heat Gain Coefficient (dimensionless, typically between 0 and 1)
- Window Area = Area of the window or glazed surface (square feet or square meters)
Solar Radiation = Incident solar radiation on the surface (BTU/ft² or W/m²).
Expanded Formula with Transmission Factor
Some calculations include a transmission factor (T) to account for additional influences such as angle of incidence or shading:
Q=I×A×SHGC×TQ=I×A×SHGC×T
Where:
- Q = Solar heat gain (BTU or Watts)
- I = Solar radiation intensity (BTU/ft² or W/m²)
- A = Window area (ft² or m²)
- SHGC = Solar heat gain coefficient
- T = Transmission factor (accounts for shading, angle, etc.)
Key factors that influence solar heat gain include:
- Glass type and coatings
- Frame materials and design
- Window orientation and size
- Local climate conditions
- Seasonal sun angles
SHGC Ratings and Performance
SHGC ratings typically range from 0.2 to 0.8 for residential windows, with each increment representing significant differences in energy performance. A lower SHGC rating means less solar heat enters your home, which proves beneficial during Ontario’s warm summers when cooling loads become substantial.
However, the optimal SHGC depends entirely on your specific situation. For south-facing windows in heating-dominated climates like northern Ontario, a higher SHGC rating can actually reduce heating costs by allowing beneficial solar gain during winter months.
| SHGC Range | Solar Heat Gain | Best Applications |
| 0.2-0.3 | Very Low | West/South windows in cooling climates |
| 0.4-0.5 | Moderate | Balanced climates, most orientations |
| 0.6+ | High | North windows, heating-dominated areas |
The Relationship Between SHGC and U-Factor
Understanding both SHGC and u factor ratings is crucial for comprehensive window performance evaluation. Whilst SHGC measures solar heat gain, the u factor indicates non solar heat transfer through conduction, convection, and radiation. Lower u factor ratings mean better insulation properties.
"When selecting windows for Ontario homes, we always consider both SHGC and U-factor together," explains Cherry Jian, our Senior Sales Consultant. "A window might have excellent solar control but poor insulation, or vice versa. The best replacement windows balance both characteristics."
For optimal energy efficiency, most Ontario homes benefit from:
- Low U-factor (below 0.3) for excellent insulation
- Moderate to low SHGC (0.3-0.5) for balanced solar control
- Low air leakage ratings for minimal drafts
- High visible transmittance for natural light
NFRC Labels and Energy Star Certification
The Fenestration Rating Council NFRC requires manufacturers to test windows under standardised conditions, ensuring accurate performance comparisons. These labels display four key metrics:
- U-Factor: Heat transfer resistance
- SHGC: Solar heat gain coefficient
- VT: Visible transmittance for natural light
- Air Leakage: Resistance to air infiltration
ENERGY STAR certification indicates windows meet strict energy performance criteria for specific climate zones. In Ontario, ENERGY STAR windows typically feature U-factor ratings below 1.6 and SHGC ratings appropriate for our mixed climate conditions.
Choosing the Right SHGC for Ontario Climate
Ontario’s climate varies significantly from Windsor’s moderate conditions to Thunder Bay’s harsh winters. This diversity requires careful consideration when selecting appropriate SHGC ratings for different applications.
For most GTA homes, we recommend:
- South-facing windows: SHGC 0.4-0.5 for balanced performance
- East/West windows: SHGC 0.3-0.4 to reduce morning/evening heat
- North-facing windows: SHGC can be higher (0.5+) since direct sun exposure is minimal
- Skylights: Lower SHGC (0.3 or less) due to intense overhead exposure
"We've installed thousands of windows across the GTA, and climate-appropriate SHGC selection makes an enormous difference in customer satisfaction," notes Eugene Siukayev, our Project Manager. "Homeowners immediately notice improved comfort and lower energy costs when windows are properly specified."
Advanced Window Technologies and Solar Control
Modern window technologies offer sophisticated approaches to managing solar radiation whilst maximising visible light transmission. Low-e windows feature microscopic metallic coatings that selectively filter solar energy whilst maintaining clarity.
Our manufacturing facility utilises advanced glazing technologies including:
- Dual low-e coatings: Enhanced solar control and insulation
- Gas fills: Argon or krypton for improved thermal performance
- Warm-edge spacers: Reduced heat transfer at glass edges
- Multi-pane assemblies: Triple glazing for extreme performance
| Technology | SHGC Impact | U-Factor Benefit | Cost Factor |
| Single low-e | Moderate | Significant | Low |
| Dual low-e | High | Very High | Moderate |
| Triple glazing | Variable | Excellent | High |
Installation and Performance Optimisation
Proper installation significantly affects actual window performance compared to laboratory ratings. Air leakage around poorly fitted windows can negate the benefits of excellent SHGC and U-factor ratings. Our certified installation teams ensure windows perform as intended through meticulous attention to sealing and weatherisation.
"Quality installation is absolutely critical," emphasises Alexandr Naumov, our Senior Project Manager. "We've seen expensive, high-performance windows fail to deliver expected results due to poor installation practices. That's why we maintain dedicated service teams with specialized tools and extensive training."
Making Informed Window Decisions
For Ontario homeowners seeking energy efficient windows, focus on comprehensive performance rather than individual metrics. Quality windows from established manufacturers, properly installed and suited to your climate, provide decades of comfort and energy savings.
Whether you’re planning new construction or considering window replacement, understanding SHGC helps ensure your investment delivers maximum value through improved energy performance and enhanced home comfort.
Frequently Asked Questions About SHGC
Is .23 SHGC good?
Yes, 0.23 SHGC is excellent for reducing cooling loads in Ontario summers. This lower the SHGC rating minimises the amount of solar heat entering your home whilst maintaining good visible transmittance VT for natural light.
Is .30 a good U-factor for windows?
Absolutely. A 0.30 U-factor represents superior energy performance with excellent condensation resistance. The lower the U-factor rating, the better insulation properties your windows provide, making this an outstanding choice for Ontario’s climate.
What is a good solar heat gain coefficient?
For Ontario homes, SHGC between 0.25-0.40 balances solar control with beneficial winter heat gain. The optimal rating depends on window orientation and your specific heating versus cooling priorities throughout the year.
Is it better to have a higher or lower SHGC?
Generally lower SHGC values work better in Ontario, reducing unwanted summer heat whilst controlling the amount of solar heat year-round. However, north-facing windows can benefit from slightly higher ratings for winter warmth.
