Clera Windows + Doors Blog

Is Condensation On Windows Bad?

Condensation forming on glass is a common occurrence for many Canadian homeowners. It comes with the territory of living in colder climates! However, it often prompts a simple yet perplexing question: Is condensation on windows bad?

In the realm of home maintenance and comfort, window condensation inside your home or between panes can be a source of concern and curiosity. Is it merely an innocent sign of temperature differences, or does it signal potential problems lurking in your home?

In this blog, we’re going to delve into condensation inside windows, as well as on the outside and interior glass. We’ll discuss the causes, implications, and if or when you should consider getting a full window replacement.

Reasons Why Window Condensation Occurs

The kind of condensation that’s damaging to your home doesn’t come from cooking or boiling water over the stove. Rather, it’s when moisture is blocking most (if not all) of your window glass with fog or frost.

When you understand how and why this occurs, you’ll be well prepared to prevent it from happening. Let’s break it down by looking at condensation on external glass, internal glass, and moisture in your window.

Window condensation caused by cold weather

External Glass Condensation

Excess moisture on the external side of the glass happens when the air outside your home is humid and warmer than your window. It happens mainly during the summer when homeowners have their windows shut and air conditioning units on.

Exterior window condensation is actually a good thing. It means your windows are doing a good job of insulating your home by ensuring humid air stays outside. That said, you should still wipe away the moisture found outside to avoid water stains.

Internal Glass Condensation

As you ask yourself “is condensation on windows bad?”, we’ll tell you that window condensation inside your house should stir caution. When the window glass becomes a cold surface more frigid than your home’s temperature, it means the humid air inside your home will turn into moisture as it touches the interior side of the cold glass.

While this kind of window condensation means your window glass is still preventing heat loss by ensuring indoor air can’t get out, it might also mean your home’s ventilation system is not working as intended.

Condensation Inside Windows

While window condensation inside your house or on the exterior glass isn’t always a problem, condensation appearing between double or triple panes means your insulated glass unit (IGU) is no longer sealed. That is a problem.

A well-sealed IGU improves insulation within your home and helps reduce energy costs. But once this seal is broken, the glass unit’s insulating air or gas is already lost and cannot provide its full range of benefits.

Steps to Reduce Condensation Inside Windows

Whether your glass is double or triple pane, there are several things you can do to prevent condensation inside windows.

  1. Improve Ventilation for Appliances

Appliances like ovens, dryers, and radiators require a proper ventilation system to regulate the amount of heat and moist air they push into your home. Consider installing a high-functioning ventilation system for these appliances.

  1. Have Your HVAC System Checked

Modern HVACs have humidifiers and dehumidifiers to keep the home comfortable. Defects or poor installation can lead to raised humidity levels and poor air circulation. Have your HVAC units checked by a professional regularly to avoid this.

A window covered in condensation with several streaks on it

  1. Take Plants Outside

Though house plants may not strike you as a culprit, the moisture dripping from their leaves and the soil increases the risk of mould growth in your home. They can often lead to window condensation inside your home.

This is because moisture combined with warm air creates an ideal breeding ground for bacteria to thrive, especially when your house plants are placed near your windows. Consider taking your indoor plants outside when you have condensation inside windows.

  1. Set up a Dehumidifier

For spaces in your home not connected to your HVAC unit—such as your basement or attic—consider purchasing a standalone dehumidifier. These take the moisture out of the air to help keep humidity levels balanced. Installing one of these will also protect your house against issues such as mould and mildew.

  1. Replace Your Insulated Glass Unit

When window condensation cannot be solved by the methods above, it might be time to replace the insulated glass unit. Choose windows with low-E glass coating when getting a replacement to maximize your investment.

Condensation Inside Windows? Call Clera!

So, is condensation on windows bad? As you’ve learned, it all depends on where the moisture appears and what you do about it. Window condensation inside your house isn’t always a big deal, but moisture inside your window is often a serious issue.

Clera Windows + Doors is the most trusted window and door manufacturer for Ontario homeowners. If condensation inside your windows has you considering a replacement, we have the solution. Our collection of slider and hung windows are armed with triple-fin weatherstripping and built-in anti-microbial properties, meaning no mould and better air quality.

Contact us today to 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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