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Is Condensation on Windows Normal?

Yes. It’s not unusual to have condensation on your house windows, but only to a certain extent. 

This phenomenon is particularly common in extreme weather conditions, that is, during winter or summer. Now, depending on the season, the fog may form on the inside or outside of your windows. 

In the following post, we provide detailed answers to these questions:

  • How much condensation on windows is normal?
  • What causes condensation on windows in winter?
  • Why do house windows fog up on the outside?
  • Is it okay to have condensation on the window sill?

How much condensation on windows is normal?

If you notice a little bit of condensation on your windows in winter, this is perfectly normal. But if your windows are constantly wet, this should be a cause for alarm. It means the air in your home is extremely humid, and you should look for ways to lower it. 

Ideally, the humidity level in your home should range between 30 and 50%. Anything above 60% can cause severe damage to your home, such as: 

Encouraging the growth of mold and mildew

High moisture levels create an environment where mold and mildew thrive. 

The biggest problem is that under the right conditions, these fungi can settle and continue growing on any surface; be it fabric, wood, glass, plastic, or paper. The term ‘right conditions’ here means the air is moist and warm. 

If the mildew forms in high numbers, then it may trigger breathing problems, aspergillosis, and allergic reactions. 

Wrecking paintwork and peeling wallpaper

If you love to decorate your home with paintings and wallpaper, then you should definitely be worried about the humidity levels in your home.

Your wallpaper is usually attached to walls using some type of adhesive. But when the environment is too humid, the excess moisture makes it difficult for the wallpapers to stick. 

Rotting furniture, furnishings, and floors

Wooden furniture and furnishings give your home a rustic and vibrant look that can’t be achieved using other types of material.

Unfortunately, these wooden fittings are also very susceptible to excess moisture. If exposed to this condition for too long, they start to rot. If this problem persists, it may cause irreversible damage on your furniture, hardwood floors, and window frames. 

What causes condensation on windows in winter?

Condensation takes place when warm air comes into contact with a cold surface, or when there’s very high humidity. 

This process occurs mostly in winter when you have your central heating system switched on during the chilly hours of the morning or evening. 

Other than this appliance, day-to-day activities like showering, cooking, and drying clothes also release warm moisture into the atmosphere. As soon as this moisture-filled warm air collides with a cold surface, it’s cooled instantly. This converts the air into beads of moisture or tiny liquid droplets that cascade down the chilly surface, in this case, your windows.  

While condensation isn’t a big deal in summer, it can be problematic in winter. This is because the humidity level in your home skyrockets in the colder months. The act of cranking up your heating system while simultaneously keeping your windows shut contributes significantly to the higher humidity levels.

Why are house windows fogging up on the outside?

When subjected to certain conditions like high humidity levels outdoors, still air, and a clear night sky, your house windows may start fogging up on the outside. 

These factors cause the temperature of the window panes to fall below the dew point. Dew point is the temperature at which air becomes completely saturated with moisture.

The resulting temperature differential causes condensation to occur on the exterior of your windows. Important to note though is that this is a natural phenomenon and it shouldn’t be a cause for concern. 

So contrary to popular belief, fog forming on the outside doesn’t mean that your newly installed windows are faulty. Rather, it’s simply the result of the temperature differences between the outdoor air and that of your window panes. 

Is it okay to have condensation on the window sill?

It’s not okay to have too much condensation on your window sill. 

Not only can it cause rotting (if the window sill is made of wood), but it can also cause mold to start growing on the surrounding walls. 

If you’re looking for ways to protect your window sill, here are a couple of suggestions:

Use a mildew-resistant paint

Be very careful when choosing the paint to use on your window sill. For the best outcome, look for one that’s resistant to mildew. This way, you’re guaranteed that no mildew will start forming on the sill as you look for ways to control the amount of condensation. 

Invest in a dehumidifier

Place the dehumidifier in a central spot in your house. 

This will serve to draw any excess moisture that finds its way into your home, and subsequently, prevent condensation from occurring on your window sills. Remember to empty the dehumidifier regularly, to ensure that it works efficiently. 

Run the thermostat above 70°

Another trick that prevents condensation from forming on your window sill is to set your thermostat to operate at above  70°. What this does is that it prevents moisture from accumulating in your home; hence, keeping condensation at bay. 

Clean your window sill regularly

It’s important that you clean your window sills on a regular basis. This helps you get rid of any mold and mildew that may have formed, due to the excess moisture levels. 

To clean your window sill effectively, you’ll need a vacuum (to remove any dust present), a spray bottle, and a microfiber cloth. Fill the spray bottle with a dishwashing liquid mixed with water, and gently spritz it on the surface. 

If there’s already a bit of mildew growing on the window sill, this simple cleaning solution won’t cut it. Instead, consider using a solution made up of one part bleach and three parts warm water. 

How to keep house windows from fogging up on the outside

Since exterior condensation is a natural phenomenon, there’s not much you can do about it. As the weather warms up, the condensation will slowly evaporate from your windows. So all you can do is be a little patient. 

If anything, the outside condensation is a simple indication that your windows are working optimally to retain heat inside your home. If the reverse happened, whereby no condensation occurred on the outside, it would mean that your windows are allowing heat to escape. 

Nonetheless, if the fog on the exterior is a bother, you can always wipe down the windows. If the windows are at street level, they shouldn’t be too difficult to reach. If they’re too high up though, ensure you use a ladder.

Wrap Up

It’s not unusual for condensation to occur on your windows, both on the interior and exterior. If it occurs on the inside, it’s the result of warm humid air colliding with a chilly surface like your window. And if it occurs on the exterior, it’s probably because of the difference in temperature between the window panes and the outside air. 

NOTE FROM the author

It's a pleasure to have you here! We've written helpful information on all things that make your home so very special.

If you really enjoyed this article, please feel free to check out the entire website. I'm super excited to share more content to help you unleash your home!

- Tiffany B.