Lots of homeowners call up window contractors to ask: What’s up with this fog on my windows? Weren’t they supposed to be Energy Star rated and keep me and my family insulated? It is a legitimate question, but the answer isn’t that simple as condensation can occur for a number of reasons.

Some of them will require immediate window replacement while others do not have to do anything with the windows. So what’s up with that unwanted fog? Here is our short report on what is condensation:

Window Condensation

The same way little droplets of water form on a cold glass Coca-Cola bottle on a hot sunny day is the same way your window fog up. Basic chemistry laws say this: water can be found in all 3 forms: liquid, gas and solid. Now, If evaporated water (gas) meets a surface colder than its temperature, it will condense or transform into tiny water drops (liquid).

In the summer, air temperature and humidity levels are high and when you pull out an ice cool glass bottle out from the fridge, that warm air will condense onto the surface of the bottle, creating water drops.

The exact same reaction happening to cold Coca-Cola bottles happens to windows as well. But, in our homes, the situation is slightly different as there are exterior, interior and intermediate condensations. So which one is dangerous and which is fruitful?

Exterior Window Condensation 

In our homes, windows are the most vulnerable to outside weather as walls have many panels and insulator cavities which prevent temperature changes. But windows are only made of glass and thin frames and when the weather gets cold outside, they get cold too. That’s why on a chilly winter morning we usually have window condensation.

Overnight, the windows were exposed to stone cold weather and when the sun rises, the air outside gets instantly warmer. However, the windows have a harder time with heating up so the warmer air condenses on the cool window glass surface.

This type of window condensation is found only on the outside surface. It doesn’t represent any dangers for our homes. In fact, exterior condensation means that your windows are doing their job right, insulating every possible air breeze while fighting temperature changes and climate shifts. Everything they face is just to keep you safe and warm.

Interior Window Condensation

Unlike exterior condensation, the interior might even be a sign for window replacement. There are many reasons for interior window condensation and they vary from broken glass sealant to improper home ventilation. Here are some of the causes and what actions you should take in preventing this process:

Old Windows

If your windows are cracked, rotten or loose then they are prone to interior window condensation. Change old windows as soon as you get the chance because fog is only the beginning as other negative consequences are mold growth, wall cracks and pesticides leading to an asthma attack, allergies and higher electricity bills.

Poor Drainage System

On especially rare occasions, interior window condensation can be caused by malfunctions in your drainage system. Old sump pump, leaky pipes, roof damage, broken gutters, tree roots clogging the sewer line…. You name it. All of these can increase moisture in your inside which will immediately stick to window glass. Check for wall cracks, leaks and unpleasant odors to see if this is what you are facing.

Type of Window

Hey, it isn’t a coincidence that homeowners have a hassle in choosing new windows. The type of window you have determines the quality of the air breeze and insulation. Awnings and casements work best for the bathroom and kitchen just because their openings allow better air breezes. You should invest in a window replacement project if the type of windows does not compliment your home, but rather disrupts the natural flow or air and vapor.

Insufficient Ventilation

To get back on track with our chemistry lesson, we will discuss insufficient ventilation. It is the number one reason for foggy windows in homes as water vapor builds up while we live our daily lives: taking showers, washing dishes, mopping the floor, cooking and even breathing. So the solution isn’t to stop breathing or taking showers, it is to open up those windows at least twice a day and allow new fresh air to enter our chambers.


It sounds odd, but the reason for your high humidity levels may be the plants you intentionally bought just for improving the air quality in your home. These same plants can lead to an extreme increase in moisture, therefore mold growth and allergies. You do not have to throw them away, just ventilate frequently and place them as close to the windows as possible.

New Windows

The best case scenario is that your interior condensation is happening due to new windows. It takes a full year for the windows to relax and gain confidence that they are doing their job right. But while that first year lasts, they will insulate every possible thing, keeping things trapped inside and accidentally cause fogginess on the inside.

Intermediate Condensation

The most dangerous type is the intermediate window condensation. This stands for fogginess and moisture trapped in between the glass panes of your windows. So, the most modern glass is made out of multiple panes, thus the names double-pane and triple-pane windows. These layers of glass are connected with gases either argon or krypton.

These gases are insulators because they are denser than air and retain proper heat transfer with minimizing loss. Argon and krypton aren’t dangerous for our health. In fact, they are also found in the atmosphere. But malfunctions between the panes will cause the windows to lose function as their main quality is insulation. Here is how the inside of the panes can get damaged:

Leaky Gases

Every gas in window panes leaks over time. Annually, approximately 1% of the gas fill leaks and if the window keeps those numbers tight then it will function for many years to come. But in some scenarios, either because of extreme weather or poor manufacturing, the gas pressure becomes so intense that it even results in window implosions (sudden explosion inside of the panes). The signs for your gases pushing the limits on that 1% leaks are intermediate condensation at the bottom and bent glass, toward the center.

Old Sealant

Sometimes, usually in the cases of low-quality materials, the window sealant starts to break and causes warm air or moisture to enter the inside of your windows – creating window condensation between the glass panes. This can even lead to mineral build-up and maximum reduction of insulator qualities. If this is happening to you, check with the window companies to find the best solution because sometimes applying another coating may not be enough protection.

About Element Windows and Doors

Element Windows and Doors is your top choice for window replacement, entry door replacement, and patio door replacement in Windsor, ON.

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