Why Windows Sweat During Winter – And Why It’s a problem

A Look at the Causes of Window Sweat and How to Stop Window Condensation in Winter

As winter sets in and you find yourself spending more time indoors to escape the frigid cold weather, you may come to notice that your windows appear to be…sweating?

“Why does my window sweat in winter?” you may ask. Well, when the temperature drops, it’s common for condensation to develop on windows, giving the appearance that your window is sweating.

While this may seem harmless, it can actually be an indication of poor air quality, leading to mold and damage to your home.

So to help you stop window sweating before it becomes a problem, here’s a look at the cause of window sweating, how it can affect your home, and tips on how to prevent this from happening while combatting its harmful effects.

What is Window Sweating and Why Does It Happen?

Window sweating is what happens when condensation builds up on the interior surface of window glass and droplets of water appear.

This condensation occurs when warm, moisture-rich indoor air cools against cold window glass, contracting and losing its ability to hold moisture. As a result, the condensed air leaves excess water in the form of droplets on the window pane.

Many daily activities inside the home add moisture to indoor air, including cooking, showering, breathing, drying clothes, and using unvented gas heating. Also, flaws in the home’s vapour barrier can allow moist air to seep into wall cavities and condense inside the walls as well.

Condensation can also occur between window panes when the seal between the panes is broken, or the desiccant inside the window is saturated.

Why Window Sweating is a Bad Thing

Window condensation in winter is a sign that your home has poor indoor air quality due to inadequate ventilation.

The excess moisture buildup leads to mold growth on windows, rotting wood, damaged frame finishes and plaster, and even water damage within wall cavities. And if there is excess moisture being held in the home, then the indoor air likely has more contaminants.

Poor indoor air quality also affects your health. So to protect your windows, home, and health, it’s important to stop window sweating in winter by intentionally ventilating your home and taking other steps to avoid moisture buildup.

8 Tips on How to Prevent Window Sweating and Combat the Negative Effects

Here are tips to prevent window sweating and eliminate the negative effects of poor indoor air quality.

Tip #1
Blinds, Shades, Shutters, Curtains and Coverings– Keep them opened

One of the first and easiest tip is to ensure that the glass gets proper air flow. To do so, simply make sure that you keep any window treatments such as blinds, shades, shutters, curtains and drapery open.

Tip #2
Screens – Remove them during winter

The second tip is to remove interior insect screens from any casement windows in order to get more air flowing to the glass. It is always a good practice to remove all window screens throughout your home during the winter season. Don’t forget to put them back on before summer!

Tip #3
Ventilation – Opening Windows and Running Exhaust Fans

To help reduce moisture in the air, always run your exhaust fans while cooking, showering, and taking baths. And keep the fans running for at least 15 to 20 minutes afterward as well.

Increasing ventilation in an air-tight home is as easy as opening windows by a crack and running exhaust fans more often in your kitchen and bathrooms. The exhaust fans will push stale air outside, while fresh air is drawn in through the open windows.

The only problem with this method is that it will cost more to heat your home in winter since you will lose warm air and have to heat the cold air that comes in through the open windows.

Tip #4
Heat Recovery Ventilator

A heat recovery ventilator (HRV) makes it possible to add fresh air into your home while retaining most of the heat from the stale air that gets vented outside.

HRVs combine fan ventilation with a built-in heat exchanger that will extract 75 to 85 percent of the heat from stale air before it’s exhausted outdoors. The extracted heat is then used to heat fresh air coming into your home from outside, so your home heating system won’t have to work in overdrive to heat the fresh air.

Tip #5
Replace Single Pane Windows with Insulated Glass Windows

Single pane windows are more likely to sweat in winter because they do not have any insulation between the interior and exterior, so the glass is much colder than with double- or triple-pane windows.

Single pane windows are also outdated, so they do not have the modern insulating properties of new insulated glass windows.

It is worth replacing your old single-pane windows with new insulated double- or triple-glazed windows that have a high R-value, insulated frames, and inert gas between the panes to maximize insulation, reduce heat transfer, and, ultimately, reduce condensation.

Tip #6
Add Weatherstripping

Adding weatherstripping to your windows will help prevent warm air from being drawn to the window and escaping. Weatherstripping prevents condensation buildup on windows and increases the energy efficiency of your home, helping you save on heating costs in winter and cooling costs in summer.

Tip #7
Install a Dehumidifier

A dehumidifier is a simple way to remove excess moisture from your home. Dehumidifiers vary in size and price. And some need to be turned on and off manually, while others automatically run when humidity levels rise in the home.

Tip #8
Get Rid of Mold

Removing any existing mold around the window edges will also help improve your indoor air quality this winter. Dormant mold from the previous winter can start growing again and at lower moisture levels than is normally required for new mold to grow.

To stop mold growth, take the necessary steps mentioned above to stop the source of mold—i.e. condensation. And treat the area with a registered non-bleach fungicide that will kill any existing mold. Then wipe the area with a damp rag or sponge.

If you keep your windows dry, the mold shouldn’t come back.

While window sweating is common in winter, it’s a sign of poor ventilation and indoor air quality. And it can have harmful effects on your health and the structure of your windows and home.

So follow these tips to prevent window sweating this winter and remove any negative effects, such as mold, to keep your indoor air quality healthy and free of contaminants.

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