Waking up to hazy windows can be alarming. After all, windows should provide a clear view of the outside, not make it harder to see through. Thankfully, moisture build-up on your windows – known as window condensation – isn’t always a reason to panic. In fact, it can often be a good thing!

Below, we outline what you should know about window condensation, including common causes, effects, fixes, and prevention tips. Let’s get started.

Is Window Condensation Normal?

In most cases, condensation on your glass alone isn’t something to worry about. In fact, it often indicates that your home is well-insulated.

Window condensation is a natural process that occurs when there’s a significant difference between temperature and humidity. Since windows have colder surfaces than insulated walls, they’re a common location for moisture to collect.

In Ontario, window condensation is especially common during the winter months. During these frigid temperatures, condensation can occur when the heated, moisture-laden air inside your home contacts the colder window surface. The temperature difference causes the moisture in the air to condense, forming water droplets or ice on the pane.

A similar process leads to window condensation during summer, although it’s less common than in winter. This time, the humid indoor air, combined with the cooling effects of air conditioning, lowers the temperature of your windows. When the warmer outdoor air meets the cooler windowpane surfaces, moisture can once again form as condensation.

Certain activities – like cooking, showering, and even breathing – add moisture to the air, helping create an environment for window condensation. In most cases, the condensation outside your windows will evaporate once the sun warms up the glass.

Although window condensation is typically natural, some situations are worth further investigating.

Excessive Window Condensation

A little bit of window condensation is to be expected, but too much is usually because of excessive moisture in the air.

Although every home differs, an appropriate humidity level inside your home is typically between 30 and 40 percent in the winter. This level often increases to between 50 and 60 percent during the summer. Excess humidity can lead to moisture build-up and condensation, making the air in your home feel clammy and uncomfortable. It can also contribute to health issues, such as respiratory infections.

Condensation Between the Window Panes

Window condensation most commonly forms on the interior and exterior of glass, frames, and sashes. Whether you can touch the condensation can help determine the location of your window’s moisture problem.

Run your fingers along the window’s glass pane – inside and outside, if possible. Is the visible condensation build-up being affected by your touch?

• If your touch affects the visible condensation, your window is functioning correctly. It’s preventing the transfer of temperature and humidity through the glass
• If the visible condensation is not affected by your touch, your windows suffer from a seal failure, making them appear foggy or cloudy. Moisture is entering between the panes of glass and isn’t working as intended by the manufacturer. A replacement window would be necessary if the window is old and out of warranty.

If the visible condensation is consistent and repeatedly forms on the inside of the window, you may need to check your home’s humidity levels. Maintaining ideal humidity for the season can help prevent condensation from reaching your window sills and causing damage.

What Causes Window Condensation?

There are three parts of the window where condensation commonly forms:

• On the interior,
• On the exterior, or
• Between the panes.

Each location has its reasons for condensation forming, which we’ll review next.

Condensation on the Inside of the Window

Condensation forms on a window’s interior when warm, moist air inside your home meets the cooler surface of window gla

ss. Common causes of this type of condensation include the following:

1. High Humidity Levels

When the humidity level in your home is too high, condensation may settle on windows. If this happens frequently, you should evaluate your indoor humidity levels.

When the air is very cold in winter, setting your furnace humidistat to 25 percent may help lower your hum

idity. However, ideal indoor humidity levels depend on the outdoor temperature.

2. Poor Ventilation

Inadequate ventilation in home areas where moisture is generated creates higher humidity levels, leading to window condensation. For example, a hot shower significantly increases bathroom humidity.

Proper ventilation through a ceiling fan, open window, or dehumidifier helps remove excess moisture and prevent humidity from affecting nearby rooms.

3. Poor Insulation

Poorly insulated windows allow warm air to escape from a home and cold air to enter in the winter. In the summer, the opposite happens. This temperature difference leads to condensation build-up on the window.

4. Lack of Energy-Efficient Windows

Single-pane windows were once the standard in homes. While they’re less common today, some properties still have them.

Because there’s only one pane of glass, the window will fail to maintain the desired internal room temperature if it differs from the outside temperature. Instead, the window panes are almost as cool as the outside, resulting in condensation build-up on the window.

Condensation on the Outside of the Window

One of the most common locations for condensation on windows is the exterior. If this is the case, it’s usually a good sign – your home has energy-efficient windows! Below are some common reasons for condensation on the outside of windows:

1. Tightly Sealed Homes

Installing a new roof or replacing drafty windows is great for energy efficiency. However, because these improvements create tighter seals in your home, they can also cause your home to retain more humidity. As a result, you may notice more condensation on colder surfaces after making these enhancements.

If your window condensation results from having a well-insulated home, there’s no need for concern – it’s normal

2. Weather

Weather is often to blame if moisture appears outside your windows during the morning but disappears naturally when the sun rises.

Again, there’s no need to worry if this is causing window condensation. Over time, the sun will warm up the window, causing the condensation to evaporate.

Condensation Between the Glass Panes

If you’re finding moisture between your window panes, there’s something wrong with your windows.

Failed seals can let the insulating gas leak out and allow outdoor temperatures to affect the interior, creating condensation.

Cracks or damage in window panes that allow moisture to enter can also cause condensation. You may notice the window can be foggy or even discoloured.

Effects of Window Condensation

Sure, the appearance of condensation is annoying in the immediate moment, but the long-term effects can be severe. They include:

Mould and Mildew

If damp areas are persistently left untreated, mould and mildew can form. The growth of these complex microorganisms – usually appearing as little black dots – can lead to potential health issues, like respiratory problems, respiratory infections, allergies, and asthma. A musty smell can also form.

Home Damage

Damage can occur to more than just the window – it can also affect the area around it. Wall discoloration, peeling wallpaper, and damage to soft furnishings can happen in the surrounding area.

Aesthetics and Visibility

The water droplets or thin layers of frost from window condensation can diminish your view. At the same time, window condensation detracts from your home’s visual appeal.

How to Fix Window Condensation

In general, more ventilation creates less condensation. Below, we outline how to remove window condensation, depending on its location.

External Condensation

Unfortunately, you can’t do much to prevent external condensation. However, the good news is that external condensation is typically short-lived, lasting only until air movement or the sun’s warmth dries up the moisture.

Internal Condensation

Fortunately, if you’re experiencing internal condensation, you can make several improvements. The most important step is to improve your home’s ventilation. Open your windows slightly to encourage air movement. In bathrooms and kitchens, use fans properly to prevent the moisture-laden air from travelling throughout your home. Consider using a dehumidifier to remove excess moisture.

Window Condensation Between Panes

Sometimes, faulty window pieces, such as panes, can be replaced. But in most cases, you’ll have to replace the entire window.

How to Clean Mould Around Windows

• If you notice potential mould forming in or around your windows, you can remove it with denatured alcohol, rubbing alcohol (the higher the percentage, the better), lemon juice, or distilled white vinegar.
• Apply your chosen solution to the affected area using a cloth or sponge, let it sit for a few minutes, then scrub gently and wipe away any residue. Be sure to ventilate the area well and wear gloves to protect your skin during cleaning.
• Keep in mind that if you don’t fix the underlying cause of moisture build-up, the mould will inevitably return.

Window Condensation Prevention Tips

• Prevent Moisture: Install a sump pump, fix water leaks, ensure proper grading near your home, properly direct eaves troughs, and cover exposed earth floors in basements. Limit the number of houseplants, and choose ones that help lower humidity rather than add to it. Moisture absorbers are available in various shapes and sizes and absorb condensation-causing moisture before it settles.
• Improve Ventilation: Leave interior doors open, raise the temperature setting on your air conditioner, and open drapes, blinds, and windows slightly, even in unoccupied rooms.
• Control Humidity Levels: Run exhaust fans while cooking and bathing, use a dehumidifier, and avoid hanging wet clothes inside.
• Trim Shrubbery: Promote better air circulation near windows and doors by trimming shrubbery.
• Purchase a Heat Recovery Ventilator (HRV): Install an HRV to help distribute fresh air throughout your home.
• Upgrade Windows: Invest in well-insulated, double- or triple-pane windows.

How to Prevent Window Condensation in the Winter

Which window would you like? Fortunately, you may not have to replace your windows. Especially if they are made of vinyl.

One of the best ways to prevent window condensation in winter is to replace single-glazed windows with double- or triple-glazed ones.

“Your windows will then have an internal layer of glass that’s protected from exterior temperatures and reduces condensation,” says Tony Miceli, Kempenfelt Windows & Doors co-owner. “The air in your home will also remain warmer, which helps it retain more moisture.”

If your home’s windows are already energy efficient, slightly increasing the temperature can help reduce window condensation. You should also ensure there’s adequate ventilation so water vapour can escape. A portable dehumidifier or whole-home dehumidifier can help extract excess water from the air.

How Vinyl Windows Prevent Window Condensation

Preventing mould and mildew caused by window condensation starts with maintaining a dry indoor environment.

Kempenfelt’s vinyl windows feature advanced sealing technology and durable, non-porous frames that prevent water infiltration, reducing the risk of mould growth. Additionally, double or triple-pane glass options with insulating gas layers help regulate indoor temperatures, preventing condensation from forming on the glass surface.

These features work together to keep your home dry, comfortable, and protected from potential moisture-related damage.

Determining When Window Condensation Means Windows Replacement

If window condensation remains a problem in your home despite your best efforts, it may be helpful to consult an expert. They’ll be able to determine if the condensation you’re experiencing is nothing to worry about or if it’s an indicator of a bigger issue, like the need for new windows.

“I recommend having a professional check your windows if condensation persists or forms between the panes. It can mean you need a window replacement,” advises Miceli. “Modern, energy-efficient vinyl windows not only prevent moisture build-up but are impenetrable by mould.”

Regarding window replacement, vinyl windows are the most popular option for Canadian homeowners. “A high-quality vinyl window does so much more than protect your family from harsh weather conditions,” says Miceli. “It also reduces noise, blocks unwanted drafts, and adds a layer of security to your home. Upgrading to these advanced windows allows you to enjoy long-term peace of mind and greater energy savings.”

For more information about window replacement, book a free, no-obligation consult with us today.

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Quick Takeaways

• Window condensation can occur in three places: between the panes, inside your window, or outside your window. If window condensation is on the exterior of your windows, there’s usually nothing to worry about.
• Some of the most common causes of window condensation are high humidity levels and poor ventilation.
• Window condensation can create mould and mildew, damage a home, and deter from a home’s aesthetics.
• There are many ways to prevent window condensation, including preventing excessive moisture and improving ventilation.
• If you notice mould forming, you can use specific methods to remove it. However, it will likely return if you don’t properly address what’s causing the mould.
• It can be difficult for the average homeowner to determine whether their window condensation is problematic. A free consult from a window professional can help.

If you’re considering updating your windows in the near future, you can learn more by visiting with our sales team at one of our four showrooms in Barrie, Vaughan, Newmarket, or Parry Sound. We are ready to answer your questions and guide you through the whole process from selection to installation. Contact us today at (705) 737-1554 or info@kempenfeltwindows.com to get started on your window replacement project.

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