What Causes Window Condensation (And How to Reduce It)?

Window condensation is like winter in Texas — it can arrive at different times every year. We stop hitting 90 degrees, then 50, then one day it’s a chilly 30 for a high. As the air begins to cool, we often forget that it can’t hold as much moisture. This temperature and humidity swing can cause condensation to occur. While some minimal condensation on your windows or window frames is not necessarily a bad thing, excess moisture can be very damaging to your home and your family’s health.

What Is Condensation?

Condensation, the water which collects as droplets on objects, generally occurs inside the home when it is extremely cold outside and much more humid inside. It’s all part of the water cycle. When it gets extremely cold outside, the humidity level inside needs to be reduced accordingly to avoid condensation.

Condensation typically occurs on cold surfaces inside the home, such as hinges, hardware, and the place you’ve likely seen it most — glass windows. These surfaces are cooler because they are closer to the outside, and excess moisture condensates on these surfaces much more easily.

Where Does the Water Come From?

The answer may sound like a quote from a classic horror movie — it’s coming from inside the house — but it’s not scary once you understand it. The surface where condensation has formed is not obtaining water from outside the home, nor is it making its own moisture, rather it comes from the environment inside the home. The higher the humidity percentage inside the home, the quicker a cooler surface will begin to condensate.

What Is Dew Point Temperature (And Why Does It Matter?)

Air temperature, combined with humidity level, defines a temperature at which condensation will form. This is called the dew point temperature. If condensation is forming, then the humidity percentage must be reduced so the resulting dew point temperature is below the temperature of the cooler surfaces.

For example, if the air inside is 70° F with 45% humidity, then any surfaces cooler than 48° F (calculated) will condensate. If it’s 15° F outside, then inside surfaces such as hinges or hardware would be approximately 30 degrees warmer, or about 45° F. In this same example, the 45° F temperature of the hardware is below the 48° F temperature, causing condensation to form. If the humidity percentage is lowered to 30%, then the part temperature would need to be around 37° F (calculated dew point temperature) to condensate.

Picture a glass of ice water with water droplets on the outside. Why is there moisture on the outside of the cold glass, yet the glass is not leaking? Because the air next to the cold glass has cooled to the dew point temperature and the air cannot hold any more moisture which will cause condensation to form on the outside surface of the glass.

What Causes Moisture in the Home?

Moisture in the home can be caused by people taking showers, cooking food, doing laundry, or when a large group is in a room together. With closed curtains where air movement is restricted, the air closest to the window remains cool and can also condensate. There are many everyday causes, but it’s important to know that elevated humidity can lead to mold and rot in unseen areas of the home.

How Can I Reduce Elevated Humidity?

An example of elevated humidity is a fogged mirror in a bathroom after someone takes a shower. The air is in an enclosed space and is saturated with moisture from the shower and then lays on adjacent surfaces that are cooler. Once the door is opened, the excess moisture will mix with dryer air outside and the condensation will go away.

Reducing the humidity percentage inside the home when it’s cold outside solves many problems. Higher humidity may not cause an issue when outside air temperatures are 30° and above, but when the outside temperatures drop below freezing to near zero while maintaining the same inside level of humidity, condensation will be an issue. Differences in inside and outside air temperatures, combined with different humidity levels inside will determine when condensation occurs. If moisture is collecting on the inside object, identify and reduce the cause of the excess moisture in the air.

Proper ventilation is key to reducing indoor humidity. Dehumidifiers are a good solution to help control the humidity level. And we’re also a big fan of — fans. Turn off your air conditioning and open your windows and doors when you can. Fans will help with the airflow and evaporate some excess moisture.

How Can I Reduce Window Condensation?

Have you noticed that the windows in your home are continually fogging up? Does it seem like they are collecting moisture? Are you worried about leaky windows?

Poorly installed or less energy-efficient windows allow warm air from inside the home to reach the outside glass pane, which warms the exterior glass and then dissipates the moisture on it. This is a side effect with older windows that you may not know you have.

Newer, more energy-efficient windows will not allow as much warmth from the inside to reach the outside glass pane, therefore the pane will be cooler, and it cannot dissipate the exterior condensation. Simply put, quality windows act like an insulated wall where the warmth stays to the inside.

What Are the Levels Required to Eliminate Condensation?

This Humidity Selector Chart shows the required humidity levels to eliminate condensation. These are only estimates, and factors such as airflow and insulation value can change the point at which condensation begins to form.

Armed with this information, you can make informed decisions as to whether or not it may be time to consider a window replacement for your home. When that time comes, or if you’d just like some help determining the effectiveness of your windows, feel free to give Clarity Windows & Doors a call at (817) 381-0055 or stop by our showroom in Southlake. We also offer free in-home consultations for those who want to know how effective your current windows are, or if you just want to talk about your options.

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