It’s winter—and a very cold winter at that. Just last week, Chicago experienced negative nighttime lows, while this week is averaging back out to 30s and 40s. This dramatic temperature variations have us adjusting the thermostat, and we might notice interior condensation forming on the windows.

Is winter window condensation a bad thing, and what can we do about it? Here is what you need to know about condensation on your windows this time of year:

Winter Window Condensation 101: What Causes Condensation?

Condensation is a natural occurrence. It is the result of warm air meeting cool air and collecting on a surface such as your windows. You may also notice condensation on a glass of lemonade during a hot summer day—and aren’t we all yearning for those warm, sunny days?

Bringing us back to the reality of winter, winter window condensation is also common, but there are variable reasons why this occurs.

Condensation on windows during the winter might result from:

  • Storing firewood
  • Taking a shower or running the dishwasher
  • Fish tanks near windows
  • Dryers that aren’t ventilated properly
  • Plants
  • And more

Even breathing can cause condensation.

Condensation on Windows

When condensation forms on the windows, all the above environmental factors can contribute to its presence. However, the age of the windows also plays a role. Newer windows may be subject to more condensation—which surprises many homeowners.

If you’ve recently had new windows installed and you’re finding condensation on the glass, don’t panic. This is likely occurring because the new windows are airtight. This is a good thing from an energy-saving perspective. After all, who wants drafts coming into the home when it’s 1 degree outside?

Interior vs. Exterior Condensation

It’s important to note that interior condensation is more common in the winter. However, these are the conditions that occur during interior vs. exterior condensation:

Exterior condensation occurs mostly during the summer. This is especially the case when the humidity is high outside and the interior temperature is cooler.

Interior condensation may signify that the humidity in the home is too high. If there is a lot of moisture circulating in the home, you might find more interior condensation—especially if your windows are new. When temperatures are very cold outside, it’s more likely that condensation will occur.

How to Control Indoor Humidity

If you’re having trouble with interior window condensation, taking control of indoor humidity can help. If moisture is collecting on the inside of the windows, humidity levels are far too high.

According to The University of Minnesota Engineering Laboratories, the following table shows the maximum safe humidity levels for the home:

-30 F or below -- not over 15%
-20 F to -10 F -- not over 20%
-10 F to 0 F -- not over 25%
0 F to 10 F -- not over 30%
10 F to 20 F -- not over 35%
20 F to 40 F -- not over 40%

(Assumes 70 F indoor air temperature)

By controlling indoor humidity, you can help reduce interior condensation this winter. If you have questions about your window’s performance or you’re concerned about condensation, contact us today with questions.