SHGC Explained: Managing Solar Heat Through Your Windows

While U-factor measures heat escaping your home, SHGC measures heat entering it. Understanding both ratings helps you choose windows that perform well year-round.

What SHGC Means

According to the National Fenestration Rating Council (NFRC), Solar Heat Gain Coefficient measures how much solar radiation passes through a window and enters your home as heat. It's expressed as a number between 0 and 1:

• **SHGC 0.25** = 25% of solar heat passes through
• **SHGC 0.50** = 50% of solar heat passes through

Lower SHGC blocks more solar heat; higher SHGC admits more.

The Northern Climate Advantage

Here's where Idaho homeowners get lucky. According to the U.S. Department of Energy, in heating-dominated climates, solar heat gain can actually be beneficial—it's free heating from the sun.

Unlike Arizona homeowners who need to block solar heat year-round, you can use it strategically.

Orientation-Based Strategy

Research from Lawrence Berkeley National Laboratory supports selecting different SHGC values by window orientation:

| Orientation | Recommended SHGC | Rationale |
|-------------|------------------|-----------|
| South-facing | 0.35-0.50 | Capture winter sun for passive heating |
| East/West-facing | 0.25-0.35 | Limit summer morning/afternoon heat |
| North-facing | Any | Minimal direct sun exposure |

South-facing windows with higher SHGC can reduce heating costs by 5-10% through passive solar gain, according to LBNL research.

The Practical Reality

While optimizing SHGC by orientation makes theoretical sense, the Efficient Windows Collaborative notes most homeowners prefer uniform windows throughout their home. If that's you, choosing moderate SHGC (0.30-0.40) provides a reasonable balance.

The Bottom Line

For Idaho, U-factor matters more than SHGC—but don't ignore SHGC entirely. If you're willing to specify different windows for different orientations, you can capture free solar heat in winter while limiting overheating in summer.

*Learn more about all window ratings in our complete guide: [Understanding Window Energy Ratings](/guides/understanding-window-energy-ratings)*