Understanding Condensation on Windows

By Robert Robillard on Home Maintenance

Condensation On Windows:window condensation

Can you draw hearts and smiley faces with your fingers in the condensation on the inside of your windows? If so, don’t blame your windows. High humidity in the home often causes “sweating” on windows.

Condensation is a natural occurrence on all surfaces in the home caused by excess humidity in the air. When water vapor comes in contact with a surface which has a cooler temperature (like a window), the vapor turns into visible droplets of moisture, which can be seen on the glass. This water vapor also adheres to the walls, which can be a more serious problem because it can penetrate walls and potentially cause mold or mildew buildup.

Understanding Condensation on Windows

Where is this condensation coming from in your home? According to the Window and Door Manufacturers Association, normal breathing and perspiration by a family of four adds a half pint of water to the air in the home each hour. That’s more than six quarts of water a day. Steamy showers add another half pint. Boiling water for pasta and other cooking activities can add up to four or five pints of water per day to your home. And, dishwashers, washing machines and even dryers can add several more pints of water to the air. Even poorly-insulated crawl spaces allow humidity to penetrate the house.

Windows and Water

Seeing condensation build-up on your window signals that steps need to be taken to reduce condensation in the home. When you have energy-efficient windows, the temperature of the glass helps reduce condensation buildup, but it will not prevent the buildup.  “Although there’s no such thing as a condensation-free window in high humidity conditions, insulating glass units really help reduce condensation,” says Christopher Burk, product manager for Simonton Windows. “Some thermally-efficient windows resist condensation better than others. Homeowners should look for windows with the highest R-values possible along with the lower U-values. R-value is the resistance a material has to heat flow. And, U-values give better insulating quality. Together, that means a more condensation-resistant window.”

Reducing Moisture in the Air

All homes need some moisture, but not an excessive amount. If you notice condensation on your windows or walls, try these tips to reduce the moisture in your home:

Tip #1 – Regularly use ventilation fans in bathrooms, kitchens and laundry rooms to circulate the air.

Tip #2 – Air out your home frequently by opening doors and windows to circulate airflow.

Tip #3 – Reduce your number of indoor house plants, since plant increase humidity levels.

Tip #4 – Add a dehumidifier to your home to remove excess moisture from the air.

Tip #5 – Make sure you have working vents in your attic, basement and crawl spaces.

“It’s important to remember that windows don’t cause condensation,” says Burk. “If there are high humidity conditions in your home, the windows are acting as a barrier to prevent the moisture from escaping the home. So, solve the moisture problem in the home and you’ll help reduce the condensation.”

Keeping Condensation Outdoors

While condensation on the inside of your windows indicates a problem in the home with high humidity levels, the opposite is true when condensation is on the outside of your windows. “When you see condensation on the outside of your windows, this means the insulating glass unit is doing its job — insulating your home from the rain, moisture and other environmental conditions you want to keep on the outside,” says Burk. “The best aspect of double- or triple-glazed windows is that they act as a barrier against temperature extremes. They help save on energy bills and keep the home warmer in the winter and cooler in the summer.”

Burk offers a final tip for homeowners related to replacing windows. “Sometimes homeowners will see more condensation on recently-replaced energy efficient windows than on their old windows,” says Burk. “That’s because their old windows were probably drafty and the moisture was escaping through the small air gaps. Once the home has more energy-efficient windows in place, the humidity is ‘locked in’ the house and doesn’t escape through the cracks.  Make no mistake … the energy-efficient replacement windows are far better for the home and energy bills than leaky windows. It just means that homeowners need to be more vigilant about reducing the humidity levels in the home.”


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About the author

Robert Robillard

Carpenter / Remodeler / Editor

Rob Robillard is “The Concord Carpenter” Rob is a builder, general contractor, carpenter, woodworker, and editor of Concord Carpenter and ToolBoxBuzz As a General Contractor and carpenter, Rob owns and operates Concord Carpenter LLC. A full-service remodeling and construction company. Rob is a recognized leader in home building best practices and a source for how-to information for building professionals. On this website, Rob covers all aspects of home construction, building science, home improvement, woodworking, remodeling, and some of the best product and tool reviews. Rob is in charge of our Tool and Product Review series - Concord Carpenter Videos where we post all of our tool reviews and video tutorials. Rob approaches remodeling and building construction with a pragmatic and problem-solving approach. He enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the construction and remodeling industry. He's a strong advocate for "raising the bar" in the construction trades and promoting the trades to youth. #BeAMentor #Green2Great Craftsmanship, quality, and pride guide his journey on this channel The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob

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