Managing Interior Condensation on Windows and Doors: A Guide for Homeowners

Interior condensation on windows and doors is a common issue in airtight, energy-efficient homes, particularly in homes with high-quality PVC windows like those from Dayside Windows & Doors. Homeowners may notice condensation more often on new windows compared to older, draftier models. Although condensation can be frustrating, it is essential to understand its causes and learn how to manage it. This guide will help homeowners reduce condensation and explore solutions for persistent issues.

Why Do I Have Condensation on My New Windows?
Energy-efficient windows, such as Dayside windows, are designed to be tightly sealed to prevent heat loss. While older windows allowed moisture (i.e. humid air) to escape, newer PVC windows keep the warm, humid indoor air inside the house, making condensation more likely to occur. The issue is not with the windows but with warm, moist indoor air coming into contact with the cold surface of the glass.

The cold glass surface, especially near the bottom of the pane, cools warm air, causing moisture to condense. This is similar to the condensation that occurs on the outside of an ice-cold drink in the summer. Even windows with upgraded Low-E glass that reflects heat inside may still show condensation if indoor humidity is high or if window coverings block air circulation that would warm the interior glass.

What Causes Interior Condensation?
High Humidity Levels
Humidity is the leading cause of interior condensation. Everyday activities like cooking, showering, and laundry add moisture into the air, continually raising the indoor humidity if not exhausted to the outside. For instance, the regular daily activities of a family of four can add up to 9 litres of moisture into the air of their home. When outdoor temperatures drop, moisture condenses on cold surfaces like windows, especially during sudden temperature drops.

Window Design and Performance
Certain windows are more prone to condensation. Good-quality casement, awning, and fixed/picture windows provide the tightest seals, reducing air leakage and the chance of condensation. Double-pane Low-E windows filled with argon gas stay warmer, reducing condensation, while triple-pane windows that have 2 or 3 of the three panes with Low-E coating provide even better insulation and greatly reduce condensation from occurring.

Curtains and Blinds
Certain window coverings can block warm indoor air from warming up the interior glass surface, allowing the glass surface to cool and causing condensation to form on the glass. This often happens at the bottom of the window where the temperature difference is most noticeable and is due to the basic scientific principle that warm air rises and cold air falls.  In this situation, the cooler air is stopped by the bottom of the window frame, where it then condenses. These window coverings would include certain blinds, California shutters, and heavy, light-blocking curtains.

6 Ways to Reduce Condensation in Your Home
Homeowners need to manage indoor humidity and improve air circulation to reduce condensation. While a small amount of condensation is natural, excessive moisture can lead to frost, ice, and damage to the window and/or trim. Here are practical steps to reduce condensation:

1. Control Indoor Humidity
Indoor humidity should be adjusted based on outdoor temperatures. As temperatures drop, indoor humidity should also decrease. A furnace humidifier should be lowered in cold weather or even turned off completely if there are other sources of humidity being added (i.e. laundry, showering, cooking, etc.). As the temperatures change, so too should the humidity in your home. For example, if outdoor temperatures are between -24°C and -18°C, indoor humidity should be adjusted to be around 25%.

2. Use Exhaust Fans
Proper ventilation is key, especially in moisture-heavy areas like kitchens and bathrooms to help reduce indoor humidity. Use exhaust fans that vent outside to reduce moisture. Opening windows briefly after cooking or showering can also help to vent the moist air.

3. Keep Air Circulating
Maintaining airflow throughout the home helps prevent condensation. Ensure that floor heat registers near windows are fully open. Running the furnace fan, even when the heat is off, can reduce stagnant air and temperature fluctuations. Homes with two-speed furnace fans can run the fan on low when the furnace isn’t heating.

4. Adjust Your Thermostat
Consistent indoor temperatures help control humidity levels. Lowering the thermostat for extended periods can increase humidity since cooler air holds less moisture. During cold weather, keep the thermostat slightly warmer to dry out the air.

5. Open Curtains and Blinds
Ensure window coverings allow air circulation by keeping them at least 3-4 inches away from the window. In the evening, leave blinds or curtains slightly open to allow warm air to reach the glass.

6. Ventilation in Older Homes
In older homes where cold air returns may be located only in hallways, keep doors open or install door vents to improve airflow. Raising bedroom doors at least 1½ inches off the floor can help as well.

Advanced Solutions for Persistent Condensation Issues

Install a Heat Recovery Ventilator (HRV)
A heat recovery ventilator (HRV) continuously replaces indoor air with fresh outdoor air, reducing moisture and improving air quality. This system is especially helpful in tightly sealed, energy-efficient homes. A DIYer with the right tools can purchase an HRV system from their local hardware store and install it themselves.  For those who prefer to leave it to the professionals, this can also be installed through a reputable HVAC company.
 
Upgrade to a Two-Speed Furnace Fan
A two-speed fan keeps air circulating even when the furnace is not heating. This ensures consistent airflow and helps control indoor humidity.

Use Dehumidifiers
Placing dehumidifiers in moisture-prone areas like basements can help reduce humidity, especially important in the fall before the cold weather starts. Dehumidifiers are designed to be most efficient when the humidity is 50-70%. Using a hygrometer to monitor indoor humidity can also aid in maintaining proper levels.

Ensure Proper Venting
Check all venting systems, including those for kitchen and bathroom exhaust fans and clothes dryers to ensure they are venting outside. Annual inspections of dryer vent hoses will help prevent blockages that can trap moisture inside the home (and which can also be a potential fire hazard).
 
In Conclusion
Managing condensation involves balancing indoor humidity and air circulation. By implementing these strategies and maintaining proper ventilation, homeowners can reduce condensation, protect their homes, and enjoy the benefits of energy-efficient PVC windows. A small amount of condensation is natural, but excessive moisture can be controlled through preventive measures, ensuring your home remains comfortable and dry year-round.

RSS Feed