Clera Windows + Doors Blog

Is Condensation on Windows Bad?

Window condensation can happen in virtually any season of the year. The burning question is: Is Condensation on windows bad? Well, this largely depends on where you find window condensation. Is it on the outside or inside? Or is the condensation or moisture on inside of windows or between the glass itself?

By first establishing where exactly the window condensation forms, you are one step closer to identifying what causes condensation on windows for your home. As a spoiler, the only really good kind of window condensation is the one on the outside of the window. Why is window condensation bad, otherwise? Read on to learn more! 

Let’s begin. 

 Photo of window condensation on the outside of the window

What Causes Condensation on Windows? 

In essence, window condensation occurs when the humidity in the air comes into contact with a cold surface. Now let’s talk about how window condensation takes place, depending on where it forms. 

1. Condensation on the Outside of Windows

So what causes condensation on windows when the moisture is on the external side? Simple. This happens when the air outside your home is humid and is warmer than your window glass. 

Therefore, exterior window condensation typically happens during the summer – a season wherein homeowners have their windows shut and their AC’s on. But why is window condensation good news in this scenario? 

Outside window condensation means that your windows are doing a good job at sealing and insulating your home. Here’s why:

  • Outside humidity stays outside – which is why the condensation is formed outside
  • The glass is insulating very well since it is colder than the outside – meaning it is not transferring outside heat so easily
  • All in all, your AC doesn’t have to work extra hard because of your window’s ability to seal the home. 

But apart from the good news mentioned above, we understand that you still want to wipe away external condensation to see the view outside. Wiping or cleaning is one way to get rid of external window condensation. The other way is to wait for the sun to point at the foggy window as this would clear up the condensation as well.  

2. Condensation or Moisture on Inside of Windows 

Window condensation is only bad when it’s on the interior side of the window or in between panes. So now, let’s discuss the first type of “bad” window condensation. 

But before we proceed, take note that condensation or moisture on inside of windows is generally not bad if it is tied to the following events: 

  • Steam coming from the shower
  • Excess steam coming from the kitchen with the ventilation hood turned off
  • Extensive use of a steam iron within a confined space
  • And other similar events. 

However, if window condensation forms on the interior side of your window without any direct cause, it could mean that your home’s humidity is too high. Therefore, the moment that the glass becomes colder than your home’s temperature (e.g. during nighttime or during winter), the home’s humid air will then form condensation as it touches the interior side of the glass. 

In the above scenario, the good news is that your windows are keeping your home sealed because after all, internal humidity cannot get out. The bad news is there could be a problem with your home’s ventilation system

High internal humidity doesn’t just cause annoying window condensation, it can also lead to the following: 

  • The formation or proliferation of mould or mildew
  • The increased presence of mould or mildew which can cause symptoms like respiratory irritation, skin irritation, and the like
  • Excess moisture in the home’s air contributes to the deterioration/swelling/rotting of wooden components as well as the corrosion of metallic components. 

For further details on how to mitigate/stop this type of harmful window condensation, go to this section

3. Window Condensation Between Panes 

So, we’ll cut right to the meat of the topic: why is condensation on windows bad if it appears between the window’s double/triple panes? Answer: Because this means that your insulated glass unit is no longer sealed. 

To further explain why condensation appears within an insulated glass unit (IGU), which is typically double-glazed or triple-glazed, we need to talk a bit about the parts of an IGU.

 As an example, if you have an IGU that is double-glazed, then that means it has the following: 

  • Two parallel panes of glass
  • A platform where the panes of glass are set on
  • Air, argon, or krypton to add further insulation between the glass
  • A seal around the glass

A sealed IGU is able to insulate your home and save extra energy; moreover, the interior side of the IGU does NOT come into contact with outside air, AT ALL. However, an IGU wherein the seal is broken means 4 things: 

  • The glass unit can no longer provide the full range of benefits anymore,
  • The window could be leaking through the faulty IGU
  • The insulating air, argon, or krypton is already lost, and
  • The outside air is able to come in contact with the IGU’s interior, causing condensation between panes 

What should be done when faced with this type of window condensation? Read the next section to find out! 

Window condensation between the window panes of a double-glazed window

How Do You Stop Condensation or Moisture on Inside of Windows or Between Panes? 

Now that we’ve finished our thorough discussion on what causes condensation on windows, let’s talk about the next steps for the bad or problematic types of window condensation.

1. What To Do About Moisture on Inside of Windows 

Modern HVACs have humidifiers and dehumidifiers to keep the home comfortable. When this is defective or if poorly set, the result could be high humidity. To put a stop to window condensation on the internal side of the glass, have your HVAC settings or functions checked by a professional. 

As for areas not connected to your HVAC (e.g. the basement, the attic), you can instead purchase a standalone dehumidifier for that area. 

And lastly, are you worried about the state of your windows? Don’t be. The good news in this scenario is that they are sealed well enough to keep humidity in. Once the humidity issue is resolved, you’ll have added comfort in your home once again – sans the inside window condensation! 

2. What to Do About Condensation Between Glass Panes in Your Double/Triple Glazed Window

As we’ve discussed in the previous section on what causes condensation on windows,  condensation between the window’s glass happens because of a leaky insulated glass unit. Therefore, when this happens, you essentially have two options: 

  • Get the insulated glass unit replaced – this is the quickest and easiest option. 
  • Get the entire window replaced – this could be the better option if you are seeing a widespread failure of IGUs from the same substandard manufacturer. It could be time for a change.

Durable, Energy-Efficient, and Stylish Windows For Your Home 

In this article, we answered a very common question asked by homeowners: is condensation on windows bad? As we’ve talked about, it isn’t always bad. In some cases, window condensation is a sign that the window is sealing the house really well. However, in some cases, condensation on the internal side of the insulated glass unit could mean it’s time to replace the window. If you’re in this situation, we’re here to help!

Clera Windows + Doors is one of the most trusted manufacturers in the fenestration industry with a good track record spanning 40+ years. We design, manufacture, customize, sell, and install our windows. All you need to do is tell us your goal and we’ll help you make it happen.

If you would like us to transform your home with durable windows that you can count on, contact us today or schedule a FREE consultation.  



  • Avatar for Jacob L. - Oakville Jacob L. - Oakville says:

    This is really helpful. I was not even aware of the rating system. This makes sense though. At least I know now to get a higher temperature window. My house is sealed up pretty well, and I could not figure out why there was so much condensation around the bases. I’ll probably be investing in a dehumidifier, and I may need to replace some windows in the near future.

  • Avatar for Michael Lan Michael Lan says:

    Great post. Yes, its definitely about turning on the heater and keeping that heat inside the house. My new replacement windows in my Toronto home has energy saving benefits, but it’s also made the house quiet too!

  • Avatar for Greg Greg says:

    Great stuff! I hadn’t stopped to think about it before, but just because my house is insulated well does not mean I am not going to have moisture buildup. I think the last tip is a great one. Opening up the doors and windows for a bit does wonders at keeping the air dry.

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