Windows are all fogged over

Here'€™s a call we receive at certain times of the year. '€œMy new windows are fogged. How can this happen when they'€™re brand new? My old ones didn'€™t do this.'€

Sometimes it'€™s a summer call, but it'€™s the Minnesota winter that really makes the phone ring. Why? They'€™re brand new windows. Today'€™s windows can be triple-glazed, low-e, argon-filled, light-reflective, energy-efficient and all that good stuff. They shouldn'€™t fog. So, why do they?

For one reason or another, the answer is physics.

Window fog culprit #1: As we build homes that are more energy efficient or '€œtighter,'€ air does not circulate like it used to with drafty windows and sparse insulation. When a home doesn'€™t '€œbreathe,'€ humidity remains inside. Showering, cooking and laundry are the largest providers of water vapor into your home. Normally, these areas have a fan installed specifically to remove these vapors. What happens to your bathroom mirror when you forget to turn on the fan while showering? It fogs immediately. When the fan is on, it clears the room rather quickly. While manufactured to put up resistance to this effect, your new, technologically-advanced windows will fog when there'€™s enough humidity present. The solution, get the humidity out with ventilation or ceiling fans to circulate the water directly out or toward exchange vents and indirectly out.

Window fog culprit #2: Actually, culprit #1 and #2 are a result of the same science, but they'€™re separated here because the things we do (or nature) to create the situation are different. In a nutshell, condensation, or dew, forms when the cold or cool surface chills the adjacent humid air and the water vapor in that air changes back to liquid water. Air has water in it. Sometimes a little, sometimes a lot (please see culprit #1). Even though your home may have a normal amount of water vapor in it, when it comes in contact with an overly chilled or overly warmed surface, condensation will appear. You know this when you open the freezer door on your warm face and your skin gets wet. The same thing happens with your window glass. When it'€™s really cold outside (think Minnesota January) and your furnace is keeping your energy-efficient home nice and toasty, warm air is rolling across your chilly windows '€“ and physics takes over. The opposite can happen in the summer, but we'€™re in Minnesota and we'€™ll let Florida worry about too much air conditioning.

What is happening in scenario #2 is that the dew point is surpassed. The dew point is the temperature to which a given parcel of air must be cooled for water vapor to condense into water. Outdoor temperatures fluctuate (Minnesota'€™s is between -40F and +100F!) which means the dew point is a moving target. When it'€™s cold outside the dew point is lower. If your home'€™s indoor temperature remains at a constant 70F and it contains a little bit of water vapor, your windows will experience condensation. This can be reduced by once again lowering the humidity level.

Even after you'€™ve explained this to your customer, they will still say '€œthese windows should guard against that. They'€™ve got Argon.'€ Well, that is correct to some extent. Single paned windows of the past continuously fogged in hot-cold exchange environments. Enter the double-paned window. They were better, allowing for the pocket of air sealed between the panes to soften the physics exchange. Now, windows are filled with the element Argon, a gas that is heavier and much slower moving than air. When Argon is heated, it takes much longer (and much more heat) for it to move to the top of the inside of the glass where all its warmth is focused at the top and the cold is focused at the bottom. If you'€™ve got a concentration of cold at the bottom of your windows, they'€™ll condense. Argon takes longer to get there '€“ but, it'€™s not infallible and when the dew point exchange is drastic enough, they'€™ll have water droplets. If you'€™ve recently updated other parts of your home such as the roof or siding, you'€™ve REALLY changed the dynamic of your home'€™s efficiency, thus its airflow. The scientific numbers before and after a remodel are drastically different.

Finally, culprit #3: Outside condensation occurs in the morning as the overnight air temperature increases and the grass doesn'€™t warm at the same pace. Dew is formed and that water is evaporating along every surface in its way. Your windows will have dew no matter how much technology has been applied.

What can you do about all of this? Start with a humidity test on the environment. Hygrometers can check the air'€™s humidity with the push of a button. They can be found at home improvement stores or online and they range from $50 '€“ $200. As mentioned before, ventilation fans and ceiling fans are designed specifically for air movement. Be sure they'€™re functioning and for more than just condensation problems'€¦restroom fans guard against mold, ceiling fans dramatically lower your heating and air conditioning expenses. Air-to-air exchangers are required in new homes and can be installed in older homes.

While all of these precautions will alleviate condensation effects, the final culprit may be a broken seal (likely under warranty) between the panes. Seal failure is usually the result of a shifting structure as a foundation moves with frost activity or earth settling. Your panes are glued together at the edges and when the seal is broken, the argon escapes and condensation occurs more frequently. One clue to seal failure is '€œdrop residue'€ between the panes. Another sign is condensation taking place on just one window in a room full of windows.

Climatologically-engineered vapor barriers, insulation inspired by NASA (really) and thermally-regulated glass have created an environment a bit more energy-efficient than the last generation of homes built in the era of Ford Pintos and disco music. However, Minnesota'€™s climate has remained the same. So, as you survive another Minnesota winter with its extraordinary set of physics, you might be able to glance at the thermometer and present a clear solution to a foggy problem.

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