Why Do My Windows Fog Up? (Condensation Explained)

Condensation on windows is a common concern when cold weather arrives. Those tiny water droplets that form on the glass can damage your windows and compromise the air quality inside your home. In this article, Fenêtres Concept offers practical solutions to help you better manage this issue.

What Is condensation?

Condensation occurs when there is a significant temperature difference between the warm air inside your home and cold surfaces like windows. When this warm air, often carrying high humidity levels, comes into contact with cooler surfaces, the moisture in the air (relative humidity) condenses into visible droplets. On windows, condensation is typically found on the lower part of the glass—this is because the lower sections of a material, such as glazing separating indoor and outdoor environments, are always colder than the upper sections.

It’s worth noting that there are different types of condensation, including surface condensation (the kind you see on windows) and hidden condensation (which can form inside walls or insulated spaces, posing invisible risks to your home).

What are the risks of condensation?

Excessive condensation promotes mold growth, which can harm the health of occupants and cause damage to materials around the windows. Such damage can lead to costly repairs or even premature replacement of installations.

Moreover, moisture on windows obstructs natural light, which is vital for adding warmth and brightness to your home, creating a comfortable and energy-efficient environment. Excessive moisture can also reduce your home’s energy efficiency, creating a cold sensation near windows and increasing heating costs. Elevated relative humidity levels demand more energy to maintain a comfortable indoor temperature, further increasing expenses.

Why does condensation appear on your windows?

Several factors can cause condensation to form. Poor home insulation, which amplifies temperature differences between indoors and outdoors, is often a culprit. For instance, single-pane windows offer minimal thermal protection compared to double- or triple-glazed windows, which create a better barrier against the cold. High indoor humidity levels, inadequate ventilation, or unsuitable window materials can also worsen the issue.

How to reduce condensation on your windows

Here are some practical tips to help minimize condensation:

• Clean Your Windows Regularly: This prevents moisture buildup on the glass.
  
  
• Close Your Windows Properly: During periods of intense cold, ensure your windows are securely shut.
  
  
• Uncover Glass Surfaces: In cold weather, remove obstructions like blinds, curtains, and interior screens to allow air to circulate on the glass surfaces, using natural convection or forced airflow within your home.
  
  
• Invest in High-Quality Windows: Opt for double- or triple-glazed windows, which provide better thermal insulation and reduce condensation risks.
  
  
• Check the Seals Around Your Windows: Damaged seals can allow cold air to enter, increasing the likelihood of condensation. Replace seals as needed to ensure proper insulation.
  
  
• Monitor Indoor Humidity Levels: Use a dehumidifier to maintain an optimal humidity level. Ensure proper ventilation in the kitchen and bathroom, and consider installing mechanical ventilation systems like air exchangers or exhaust fans for effective moisture control.
  
  
• Limit Excess Moisture Sources: Reduce activities that produce excessive humidity, such as taking long, unventilated showers or cooking without covering pots.

By following these steps, you can effectively manage condensation and protect both your windows and your indoor air quality.

Optimize your indoor comfort

If your windows are old, replacing them can be an effective solution to better insulate your home. A well-insulated front door and modern windows can significantly reduce air infiltration and help maintain a healthier indoor environment.
A Phenomenon to Consider: "There’s condensation on my new windows, even though it wasn’t present on my old ones."

Replacing your doors and windows greatly reduces air leaks, which in turn decreases air exchange between the inside and outside of your home. If your household activities generate humidity, the reduced airflow can lead to increased indoor relative humidity. During cold weather, it’s crucial to maintain the recommended indoor relative humidity levels, as shown in the table below:

Comprehensive guide to help you control humidity and protect your home

To learn more about sources of humidity in a home, check out this article: Sources of humidity in a home.

Digital hygrometers, available for under $20, make it easy to measure indoor temperature and humidity levels.

For any questions about your doors and windows or for a renovation project, trust Fenêtres Concept. Our experts provide personalized advice and high-quality service. Contact us for a quote and turn your ideas into reality!