# Why are my Windows Foggy? What You Need to Know About Condensation

- Link: https://mycoastalwindows.com/foggy-windows/
- Published: 2018-05-15T18:18:54-04:00
- Author: Jeremy Wood

**Q**: I noticed that fog sometimes forms on my windows. Is this something to worry
about, and how do I fix foggy windows?

**A**: Foggy windows are a common occurrence here in New England. You might find
moisture on the glass panes on the inside of the window as well as the outside, 
depending on the time of year. You might even notice that even new replacement windows
have foggy glass. But what gives?

## What is Condensation and Why Does it Happen?

![Foggy windows example image showing mold caused by condensation on the windows
overtime. ](https://mycoastalwindows.com/wp-content/uploads/2025/01/bigstock-Mold-
On-A-Foggy-Plastic-Window-226143352-600x400.webp)

The first step to understanding foggy windows is to learn about condensation. According
to [the US Geological Survey](https://www.usgs.gov/special-topics/water-science-school/science/condensation-and-water-cycle),
condensation is the process of when water vapor in the air is changed to liquid.
It occurs on the glass of windows when the surface is cooler than the surrounding
air. You can also experience condensation on your eyeglasses or a [cold glass of lemonade in the summer](https://mycoastalwindows.com/colors-summer-yellow-bring-sunshine/).

Since condensation is a natural part of the water cycle, it’s entirely normal to
find fog on your windows from time to time.

## When Does Condensation Occur?

The formation of condensation depends on environmental factors and sometimes the
time of year. For example, condensation commonly occurs on the outside of the window
during the summer. This is due to high outdoor humidity levels with moisture in 
the air collecting on the glass. It’s essentially the same concept as finding dew
on the grass in the morning.

However, in the wintertime, condensation may form inside of the interior glass because
the air outside is cold and the interior air is warm. This indicates that the humidity
levels in the home are quite high.

**It’s important to never ignore window condensation—_especially if it doesn’t go
away_**. Knowing why condensation is occurring on the windows is important for energy
savings. Condensation can be a major sign that the window is no longer thermally
efficient, which directly results in lost energy dollars.

## When are Foggy Windows a Problem?

![Condensation shown resulting in foggy windows.](https://mycoastalwindows.com/wp-
content/uploads/2025/01/condensation.webp)

Although condensation is a natural yet common culprit for foggy windows, there are
other reasons why you’re experiencing condensation—and it can sometimes signal a
major problem:**  seal failure.**

**These are a few red flags for problematic condensation (which typically indicates
seal failure):**

 * When you see fog on inner glass panes (that doesn’t wipe off), the seal has lost
   its argon/krypton gas. It’s filled with standard air, which lacks energy-efficient
   properties. This means the window’s insulation is gone and no longer maintains
   indoor temperature.
 * Think of it this way: with argon/krypton gas, energy moves through the gas like
   honey. If your thermostat is set to 70 degrees and it’s 30 degrees outside, air
   starts to blend since the gas is gone. Because energy travels through standard
   air faster than gas, you lose money on energy bills.
 * When you see fog inside the glass panes, the energy barrier is failing (see above
   example). It works like a cold/warm front in a weather system, allowing heat 
   to leave or enter your home.
 * With seal failures, you must carefully check for moisture on wood and vinyl windows.
   If ignored, this problem can cause moisture and mold damage. According to the
   [United States Environmental Protection Agency](https://www.epa.gov/mold/mold-course-chapter-1),
   interior condensation may also result in mold growth. This is most commonly seen
   in bathrooms. It’s important to note that lesser-grade vinyl that is not UPEC(
   [high quality virgin vinyl windows](https://mycoastalwindows.com/windows/)) is
   porous and can be prone to mold and mildew if not properly maintained. Low grade
   vinyl window frames are like the cheap plastic containers with spaghetti sauce.

### How Do I Know if Condensation is on the Inside or Outside?

If you suspect that you have condensation inside the window panes, try cleaning 
the glass first. Sometimes what is thought to be fog is buildup or dirt, especially
if this window is old or located in the kitchen.

If the fog doesn’t go away after wiping it, it is most likely between the glass 
panes and an indication of seal failure.  When this is the case, there is often 
no choice other than replacing the window. Replacing the entire window can bring
extra benefits aside from addressing seal failure, such as lower utility bills and
reduced drafts.

### Help! My New Replacement Windows are Foggy

With professional window installation, an airtight seal is created around the frame
to block out drafts and moisture. If you discover condensation on new windows, this
is often a sign that the windows are doing their job and conserving energy in the
home.

Look for virgin vinyl windows with warm-edge spacers. This is important for separating
the panes of glass that impact edge temperature, which is typically colder in the
center of the window. Condensation resistance measurements run between 1-100—the
highest numbers are most effective.

### Replace Foggy and Outdated Windows with Coastal Windows & Exteriors

![Replacing foggy windows with new high quality options.](https://mycoastalwindows.
com/wp-content/uploads/2025/01/bigstock-224535097.webp)

Coastal Windows & Exteriors services Massachusetts, southern New Hampshire, and 
Maine with quality lifetime replacement windows. If condensation is a problem with
your windows, contact us for some of the most energy efficient windows in New England.
Contact John with questions at [svanderbilt@mycoastalwindows.com](https://mycoastalwindows.com/foggy-windows/svanderbilt@mycoastalwindows.com)
or call 978-304-0495 for a quote.

[
⌊Online Booking CWE Tool⌉⌊Online Booking CWE Tool⌉