Window 101: Condensation Issues

October 20, 2015


While Green Bay is known for being “The Frozen Tundra” the last thing a homeowner wants to have is frozen windows. Unfortunately, every year when the temperatures start dropping, we start getting calls about condensation and icy windows.

 How can you tell if condensation/ice is forming because your windows are junk vs How to tell if there’s a different issue?

Let’s start with the basics: What is condensation? How can I get rid of condensation? How can I tell if the condensation I’m seeing is a window problem?

What is condensation?  In simplest terms, condensation is the liquid water (or ice) you see when the water in the air (aka humidity) is trying to get to the coolest place it can. In a well-sealed home this will be the glass of the windows. This is the reason dehumidifiers are often placed in basements; they’re cooler than the rest of the home. Relative humidity level and outdoor temperature are the two main factors that determine whether or not you’ll see condensation inside your home. If you can rule out these two variables, you can discover if your condensation issue is actually a window issue.


How can I get rid of condensation?  To get rid of condensation you need to first narrow down what could be causing it. Since moisture in the air causes it to occur, the most common places to have issues are in the kitchen, laundry room, or bathroom. People with a total home humidifier will often notice condensation in all rooms if they forget to change the setting from summer to winter or if the levels are set too high. If you’re unsure about the humidity level in your home, you can purchase a hygrometer very inexpensively to find out.

Side note: Indoor relative humidity is a catch 22 in Wisconsin. Typically people are most comfortable between 25-60% indoor humidity, although it varies from person to person. One thing to keep in mind is that relative humidity below 30% will start to cause static to build up and may cause dry skin while humidity levels above 50% can enable mold growth.

The indoor and outdoor temperatures as well as indoor relative humidity will determine when you start to see condensation on your windows. The following chart (published by Andersen®) is a good starting point to determine approximately what your target indoor humidity should be. Because Wisconsin winters are very cold, it is worth noting that at comfortable indoor humidity most likely will cause condensation.


Outside Air TemperatureMaximum Indoor Relative Humidity
-20° F or BelowNot over 15%
-20° F to -10° FNot over 20%
-10° F to 0° FNot over 25%
0° F to 10° FNot over 30%
10° F to 20° FNot over 35%
20° F to 40° FNot over 40%

Based off an indoor temperature of 70° F


How can I tell if the condensation I’m seeing is a window issue? If you’ve gotten your humidity to a reasonable level and are still seeing condensation on the windows, it is likely that a window issue is to blame. Before you can resolve the issue, you need to narrow down what is causing it. The most common causes are 1) Outdated window technology 2) Broken window seal 3) Lack of weatherstrip 4) Improperly installed windows.

                If outdated window technology is the issue: If your windows are single pane you’re losing a lot of energy (heat) through the glass. Likewise if your windows were manufactured before the 1950s (We see windows older than this all the time!), you may have two panes of glass that are just barely more efficient than one. Best fix: This is a prime candidate for window replacement. The latest technology includes an argon gas blend and multiple Low-Emissive (Low-E) coating that will insulate your windows. If window replacement isn’t an option, installing storm windows or covering the windows with insulating plastic film will help.

                If broken window seals are the issue: If your windows have a hazy or foggy appearance between the panes, a broken window seal is most likely to blame. Best fix: Consult the manufacturer to see if this is covered under warranty. If it is not, you can look at their options for sash or glass pack replacements or contact another glass replacement company. If you’re having additional issues (operational, appearance, efficiency, etc) it’s a good idea to look into total window replacement.

                If lack of weatherstrip is the issue: This issue is characterized by drafts or cold air near the area of the windows, especially where the sash (the glass and frame that move) meets the frame. If there is no weatherstrip or it is worn down, air could be seeping into your home and lowering the temperature of the glass, thus causing the condensation. Best fix: Adhesive backed weatherstrip can be purchased inexpensively at home improvement or hardware stores. Replace the old weatherstrip to see if this helps.

                If improperly installed windows are the issue: Unfortunately, this is the most difficult to repair. If your windows are hard to open or close, if you can feel a draft even when they’re locked, or if you can feel a draft from behind the wood trim, it is likely your windows were not properly installed. Best fix: Contact the builder or company that installed your windows. If this is not an option, you should consider window replacement. An improper installation can allow water to get into the frame of your home and cause extensive rot and damage if not handled properly.


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