Window Condensation Resistance: Why It Matters in Cold Climates

You've probably seen condensation on your windows during cold weather—water droplets or even frost forming on the glass. While some condensation is normal, chronic condensation indicates a problem that can damage your home.

What Causes Window Condensation?

According to the FGIA (Fenestration & Glazing Industry Alliance), condensation forms when warm, humid indoor air contacts a cold surface. In winter, if your window's interior glass surface drops below the dew point, moisture in the air condenses on it.

The colder the exterior temperature and the higher the indoor humidity, the more likely condensation will form.

The Condensation Resistance Rating

According to the National Fenestration Rating Council (NFRC), Condensation Resistance (CR) is rated from 1 to 100, with higher numbers indicating better resistance. While not required by ENERGY STAR, this rating matters significantly in cold climates.

| CR Rating | Performance Level |
|-----------|-------------------|
| Below 35 | Poor |
| 35-50 | Fair |
| 50-65 | Good |
| Above 65 | Excellent |

Why Idaho Homeowners Should Care

According to ASHRAE research, chronic window condensation causes:

• **Mold and mildew growth** on window frames and surrounding walls
• **Wood rot** in wooden frames and trim
• **Paint failure** and finish damage
• **Potential health issues** from mold exposure

In Idaho's cold winters, the temperature differential between indoors (70°F) and outdoors (sometimes below 0°F) creates significant condensation risk with poor-performing windows.

The Connection to U-Factor

Here's the good news: according to the NFRC, windows with better U-factors naturally have higher condensation resistance. When a window insulates well, its interior glass surface stays warmer, reducing condensation risk.

So prioritizing U-factor automatically helps with condensation resistance.

The Bottom Line

For Idaho homes, look for condensation resistance ratings above 50—ideally above 60 for mountain communities with extreme cold. Premium windows with low U-factors typically deliver good CR ratings as a bonus.

*Learn more about window performance metrics: [Understanding Window Energy Ratings](/guides/understanding-window-energy-ratings)*