Ice on Inside of Windows: Why It Forms and How to Prevent It

If you're a Canadian resident, you know all too well that ice on inside of windows is a regular in most homes during the winter months. But enough is enough! It's time to take matters into your own hands and get rid of that frost once and for all, right?

In this article, we'll explain why ice forms on windows, how to remove it, and how to prevent it.

Key Takeaways

• Ice forms on the inside windows when warm, humid indoor air hits the cold glass surface and condensation forms; if the surface is cold enough, that window condensation freezes. This is most common in winter or in very cold climates.
• High indoor humidity, low indoor temperatures, air leakage, cracked or poorly insulated windows, and damaged frames all increase the risk of frost. Even new windows can freeze if they’re low-quality or poorly installed or if indoor humidity is too high.
• Ice buildup can damage window frames (especially wood), promote mold growth, reduce insulation, and raise heating costs, so it’s not just a cosmetic issue.
• Prevention and solutions: controlling indoor humidity with exhaust fans, dehumidifiers, or HRV systems; sealing cracks and improving insulation (plastic film, bubble wrap, or storm windows); regularly inspecting windows for gaps or damage; replacing old or single-pane windows with high-quality, energy-efficient multi-pane units.

Why Does Ice Form on the Inside of Windows?

Ice forms on the inside of windows when warm, moisture-laden air comes into contact with the cold glass surface, causing water droplets (condensation) that, when it's cold enough outside, freeze into ice crystals. It happens during the winter and early spring, when the difference between indoor temperatures and outdoor temperatures is significant. The colder it is outside, the higher the chance of condensation becoming frost.

Ice buildup on windows is incredibly common in houses with:

• Old windows
• Single-pane windows
• Double-glazed windows with a broken seal
• Poorly installed windows
• Too much humidity indoors
• Cracked glass surfaces
• Low indoor temperatures

In other words, while old windows are definitely the biggest risk of having ice forming on them, new windows and doors can also be prone to this issue, especially if they are not installed correctly. And even if the windows are properly installed, condensation and ice can still form on them if outdoor temperatures are very low and indoor humidity levels are too high.

Factors that Increase the Risk of Ice Buildup on Windows

In the following sections, we'll talk about the factors that increase the risk of ice buildup on windows.

High Humidity and Low Temperatures Indoors

As mentioned above, two factors (that you can control) lead to ice buildup on windows:

• High humidity levels
• Low indoor temperatures

Kitchens, laundry rooms, and bathrooms are particularly prone to developing ice on windows because they generate significant moisture. But, believe it or not, ice can form on your bedroom windows as well simply because you're sleeping in that room. Breathing can also increase humidity levels!

Additionally, if indoor temperatures are lower than 20°C (68°F) and outdoor temperatures are below freezing, you can definitely expect frost on windows.

Here are the humidity level recommendations based on outdoor temperatures:

Keep in mind that, according to Health Canada, humidity levels should stay between 30% and 55%. Therefore, if outdoor temperatures are very low, it is not advisable to keep humidity levels below 30% for too long, especially if you have health issues.

Air Leaks and Window Quality

Even the tiniest cracks or gaps in window frames or glass can allow cold air to seep in. Contrary to most homeowners' expectations, this problem isn’t limited to old windows. New ones can leak too if they’re made from low-quality materials or were poorly installed.

You might notice frost forming mainly in the corners of your windows. This can often happen with frames that lack welded corners, which makes them more susceptible to air infiltration.

Windows with fewer panes are also more likely to frost build up. Single-pane windows pose the highest risk, without a doubt. Double-pane windows, while much more energy-efficient, may still develop ice in extremely cold climates. Many homeowners who live in areas where winter temperatures fall below -30°C (-22°F) confirmed that switching to triple-pane windows dramatically reduces frost.

The window design itself also plays a role. For example, casement and awning windows generally provide a tighter seal than sliding or hung windows.

And let's not forget about warped, cracked, or rotten window frames, which can really affect the window's energy efficiency.

Should You Worry About Ice Buildup on Windows?

Ice buildup on windows should definitely be addressed as soon as possible because it can affect your home’s comfort, energy efficiency, and structural integrity.

First of all, ice doesn't stay the same endlessly. It thaws, and then a new ice layer forms, and then that one thaws, and so on. This repeated freezing and thawing cycle can severely damage window frames, especially if they're made of wood. Over time, this can lead to structural damage, and even the surrounding walls can suffer.

Furthermore, this can cause mold and mildew growth on the windows, on the walls surrounding the windows, and on other surfaces in your house.

Last but not least, if ice forms on your windows, this is a sign that your windows don't insulate well, which also means that your energy bills will definitely increase this winter as poor insulation forces your heating system to work harder.

How to Remove Ice Buildup From Windows?

If you've noticed ice buildup on your windows, don't try to scrape it! This can severely damage your windows. Instead, here's what you can do:

• Let the warm room air melt the ice.
• Use lukewarm water to melt the ice. Don't be too forceful to avoid damaging the glass. Don't use hot water, as the glass can crack.
• Mix one part water with two parts rubbing alcohol and spray the solution onto the ice. Wipe it away and dry the surface.
• Mix one part water with three parts vinegar. Spray the solution onto the ice. Wipe it away and dry the surface.
• Use a hairdryer to thaw the ice, but use the lowest temperature possible.

These are temporary solution options to get you through the coldest days until you address the root cause.

How to Prevent Ice on the Inside of Windows

While you cannot control the weather outside, you can certainly control the indoor environment to prevent ice from forming on the inside of your windows. Here's what you can do!

Reduce Humidity Levels

First of all, use exhaust fans. They vent moist air outside and are particularly useful in kitchens and bathrooms. Dehumidifiers can help as well. Just make sure the units you have are suitable for the space where you need to remove humid air from. An HRV (Heat Recovery Ventilator) system could also be incredibly useful, as it exchanges moist, stale air from the inside with fresh air from the outside.

Here's what else you can do to reduce condensation and humidity inside:

• Keep the lids on the pots while cooking.
• Keep the door open while showering.
• Avoid keeping heavy drapes completely closed during the night, as moisture can get trapped between the drapes and the windows.
• Reduce the amount of indoor plants, as they can increase humidity.
• Ventilate your house properly. Open windows every day.
• If possible, keep the doors between rooms open to keep the air circulating.
• Avoid drying your clothes inside.
• Run a ceiling fan clockwise to help push the warm air down and prevent cold air pockets near windows.

Insulate Your Windows

If you're looking for a quick, short-term solution to stop ice buildup on windows, try to insulate them. You can do so with plastic window insulation film or bubble wrap, for example, or by installing exterior storm windows.

Keep in mind that if the cracks around the window are not sealed, applying insulation film or bubble wrap probably won't solve the issue.

Inspect Your Windows

If your windows are poorly insulated, you won't be able to prevent condensation and frost even if you do manage to maintain the indoor humidity levels within the recommended range.

For example, if your windows are single pane, the glass surface will always be cold. Whenever you cook, condensation will form. If there are freezing temperatures outdoors, the fog or water droplets on the glass surface will turn into ice.

Or here's another example. If there are cracks or gaps around the window frame or if the glass is cracked, any efforts to reduce moisture indoors won't suffice because cold air will get in, it will keep the glass surface very cold, and condensation will form.

Therefore, inspect your windows. If they're single-pane, that's the first sign that they need to be replaced. If they're double-pane and ice still forms on them, check:

• If there are no gaps or cracks around the frame (which you can seal with weatherstripping and caulking).
• If the frame is warped (in which case you might have to replace the window, especially if the deformation is severe).
• If the window opens and closes smoothly (in which case it might be misaligned; you can try tightening loose hardware or seeking professional help).
• If there is a sash sag issue (this happens with casement windows; in this case, you might have to replace the window or seek professional repair services).

Replace Your Windows

This is the only long-term solution that can prevent ice on the inside of your windows. Nowadays, windows are equipped with various technologies that significantly improve their energy efficiency, especially the windows manufactured in Canada for Canadian homes.

At Magic, for example, we choose to manufacture our window units right here in Ontario, so we can control their quality and incorporate the best technologies designed for Canada's climate.

Our products are among the most energy-efficient on the market because they:

• Have significantly more insulating gas between panes.
• Feature a unique operating mechanism thanks to our Parallex hardware that ensures an airtight seal.
• Have window frames with welded corners made from steel, aluminum, and vinyl, which translates into exceptional durability, strength, and energy efficiency, so the frames won't warp and crack when temperatures drop.
• Feature the best-performing warm-edge spacers and can be equipped with Low-E glass.

We also offer the possibility to equip your windows with our fully retractable solar shades and thermal blinds (the latter improve the windows' energy efficiency by 40%).

If you're curious to learn more about our windows, give us a call!

Frequently Asked Questions

How do I stop my house windows from icing on the inside?

You can stop window icing on the inside by reducing indoor humidity with a dehumidifier, running exhaust fans, and improving air circulation. Adding insulation or using thermal curtains also helps keep interior glass surfaces warmer.

Is it normal to have ice build up on the inside of windows?

It’s not normal to have ice buildup on the inside of windows, but it is common in very cold weather, especially in homes with high humidity and poor insulation. Ice forms when warm, moist indoor air meets cold window glass, causing condensation that freezes.

How do you stop condensation on the inside windows in the winter?

To stop condensation on inside windows in the winter, lower indoor humidity by using fans, opening vents, or using a dehumidifier, and keep air flowing near windows. You should also seal any cracks and gaps with weatherstripping and caulking or upgrade to energy-efficient windows if your windows are old or poorly insulated.

What causes ice to form on the inside of your windshield?

Ice forms inside a windshield when excess moisture in the air condenses on the cold glass and freezes overnight.

What problems can ice buildup on windows cause?

Ice buildup on windows can damage the frames and promote mold growth, while also causing higher energy bills since your heater has to work overtime.

Are there any quick fixes for existing ice on windows?

You can quickly melt ice on your windows with a hair dryer or apply a rubbing alcohol solution.