Using Window Orientation for Passive Solar Heating in Idaho

In heating-dominated climates like Idaho, the sun is free heat. According to the U.S. Department of Energy, strategic window selection by orientation can reduce heating costs by 5-10%.

How Passive Solar Works

According to NREL, passive solar heating is simple physics:
1. Winter sun is low in the sky
2. South-facing windows receive direct sunlight
3. Solar heat enters through glass
4. Home absorbs and stores heat

The key is maximizing winter gain while minimizing summer overheating.

Orientation-Based Window Strategy

According to research from Lawrence Berkeley National Laboratory:

South-Facing Windows

• **Recommended SHGC:** 0.40-0.50 (higher than typical)
• **Why:** Capture maximum winter solar gain
• **Summer protection:** Roof overhang blocks high summer sun naturally

East-Facing Windows

• **Recommended SHGC:** 0.25-0.35
• **Why:** Morning summer sun causes early heat gain
• **Lower priority for passive solar** (sun angle less favorable)

West-Facing Windows

• **Recommended SHGC:** 0.25-0.35
• **Why:** Afternoon summer sun is hottest and hardest to shade
• **Consider exterior shading** where practical

North-Facing Windows

• **SHGC:** Doesn't matter (minimal direct sun)
• **Focus on U-factor:** These are pure heat-loss surfaces

The Practical Reality

According to the Efficient Windows Collaborative, while this strategy is technically optimal:

• Most homeowners prefer uniform appearance
• Multiple specifications add complexity and cost
• Moderate SHGC (0.30-0.40) throughout is a reasonable compromise

Making It Work

If you want to optimize by orientation:
1. South: Specify high-solar-gain Low-E
2. East/West: Standard Low-E
3. North: Focus on lowest U-factor

According to NREL, even partial optimization (just south-facing windows) provides meaningful benefit.

The Bottom Line

Idaho's cold, sunny winters create an opportunity for passive solar heating. Higher SHGC on south-facing windows captures free heat—but only if you're willing to manage the complexity of different specifications by orientation.

*For complete guidance, see: [Climate Zone Window Selection](/guides/climate-zone-window-selection-idaho)*