ACMO Blog

What to do About Condensation on Windows

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People often ask, why do we get condensation on windows? There are several answers to that common question.

If you have old windows that have continual condensation, replacing the windows will significantly reduce the amount of condensation if you opt for high-energy-efficient windows. The good news is that new window technology offers improved insulating value and can greatly reduce condensation. High-performance windows, which have special “low-E” coatings and are filled with inert gases such as Argon, can provide considerable energy savings that are considerable.

Homeowners might experience this even with their new energy-efficient windows' outdoor condensation. This occurs when moisture from the air outside the building condenses on the surface of the windows, creating a foggy or cloudy appearance. While this can be a cause for concern for some homeowners, it is typically not a sign of a problem with the windows themselves. The windows are designed to prevent heat from escaping the building, which means that the exterior surface of the window stays cooler than it would with traditional windows. When warm, humid air outside comes into contact with the cooler surface of the window, the moisture in the air condenses on the glass, creating the appearance of fog or cloudiness. Moisture condenses out of the air onto a cold surface that is said to be below the dew point. The dew point varies with the air temperature and the amount of moisture it contains. Particularly in spring and autumn, the glass temperature can fall to a low level during the night, and the dew point can be comparatively high in these seasons. The glass temperature can be below the dew point under these conditions, and moisture can condense onto the surface. This condensation is a sign that the windows are performing well and keeping the heat in, making them superior insulating glass products.

Efficient windows have special “low-E” coatings and multiple glass panes with inert gas between them to reflect heat back into the home's interior. Under specific conditions, such as quick temperature changes and high humidity, the exterior glass surface may cool below dew point temperature and collect moisture from the outside air, resulting in condensation. This is a natural occurrence and does not indicate any problems with the window.

With modern low-emissivity glass, more heat is kept inside, resulting in a lower outer pane temperature and a greater risk of condensation on the external surface. While this may seem like a problem, it is actually a sign that the windows are functioning as intended. The condensation is a result of the windows creating a barrier between the inside and outside of the building, preventing heat from escaping and saving energy.

There are steps that can be taken to reduce or eliminate outdoor condensation on energy-efficient windows:

Increase ventilation in the room. This can be done by opening a window and increasing the airflow in the room.
Set the furnace fan to run continuously + install a two-speed energy-efficient motor.
Use a dehumidifier to remove excess moisture from the air. Reducing the amount of moisture in the air will reduce the likelihood of condensation on the windows.
Installing a heat recovery ventilator (HRV). The HRV provides the opportunity for continuous ventilation.
Monitor the furnace humidifier. The higher the indoor relative humidity, the greater the chance of condensation occurring on cold surfaces. Maintaining a desirable and healthy humidity level will reduce your risk of mould.
Run the exhaust fans for the kitchen, bathroom and laundry rooms for longer periods.
Make sure exhaust fans vent directly outside.
Reduce the number of plants in your home and water them less. They release water vapours.
Use the bathroom exhaust when showering or bathing.
Remove Interior screens on windows during cold months

Lastly, ensure that the windows are properly installed and sealed. If there are gaps or leaks around the windows, warm, humid air can enter the building and condense on the surface of the windows. Proper installation and sealing can help to prevent this from happening. New windows should also be much more air-tight due to the improved construction of the window and better, more efficient installation, sealing and caulking of your windows. Because new windows are more air-tight, the moist air in your home is less likely to escape. That means homeowners need to pay more attention to humidity levels in their homes.

In summary, outdoor condensation on energy-efficient windows is a natural phenomenon which is not frequently encountered and can be observed for a reasonably short period of time and is not necessarily a cause for concern. Homeowners can take steps to mitigate its impact with proper ventilation, using a dehumidifier. With these precautions in place, homeowners can enjoy the energy savings and other benefits of their energy-efficient windows while minimizing the inconvenience of outdoor condensation. Ultimately, the benefits of energy-efficient windows far outweigh the minor inconvenience of outdoor condensation, making them a smart and responsible investment for any homeowner.

What do we recommend as the best top-rated energy-efficient window in Canada? The Natural Resources Canada (NRCan) website rates RevoCell® windows as the highest Most Energy Efficient Star Certified windows for 2023. RevoCell® windows are made from cellular PVC and have the highest Energy Rated (ER) number of all residential windows in Canada, according to the NRCan website.

Most Energy Efficient Windows!

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