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What Causes Condensation on Windows in Winter?

From dew sparkling in the morning sun to water droplets on a soda can, all condensation is fundamentally the same: water vapor that has cooled to the point of condensing and forming liquid water droplets. This change of state occurs based on temperature, when warm humid air meets a cold surface or cool air.

Condensation is most apparent when there’s a significant difference in the temperature of a surface and of the air. For example, you may notice condensation on a bathroom mirror when exiting the shower. In this case, condensation forms because the air in the bathroom is injected with steam and heat from the shower which then condenses on the comparably cool mirror. 

So, What Causes Condensation on Windows in Winter?

As outdoor temperatures drop and the furnace kicks on, homeowners may see an increase in window condensation. Window condensation is formed in the same way condensation forms on the outside of an icy glass of water – warm, humid air meets cool window glass and condenses on the surface.

Is Window Condensation Bad?

While some condensation is to be expected, especially in bathrooms, in general, it’s best to limit the amount of interior window condensation in your home. While exterior condensation is the result of factors we can do little to mitigate, excessive interior condensation is something we can and should take steps to mitigate. Left unchecked, interior window condensation can lead to window frame damage. 

How to Stop Condensation on Windows in Winter

While it can be difficult to eliminate window condensation, there are steps homeowners can take in the wintertime to reduce window condensation in their homes. The first step to mitigating the condensation affecting your house is to identify its exact location: interior, exterior or between the panes. Read on to learn our recommendations for reducing the effects of condensation on windows in winter:

Exterior Window Codensation

In general, exterior window condensation is more of a nuisance than a problem. If you’re home’s windows are foggy or frosted on the exterior, a little patience will go a long way!

Car owners likely feel the effect of window condensation most acutely as a foggy windshield can throw a real wrench in a morning commute. If you find yourself fighting with foggy car windows every morning, check out these tips for mastering fog-free windshields.

Interior Window Condensation

Excessive condensation on the interior of your windows is not only frustrating, it can spell eventual disaster for your window frames. Reduce interior window condensation with these nine tips:

  1. Replace single pane windows.
    By nature, single pane windows are less insulated than double pane windows, also called Insulated Glass Units or IGUs. If there are still single pane windows in your home, replacing them with new, energy efficient double pane windows will reduce condensation and lower your energy bill.
  2. Always use your exhaust fan.
    From cooking to bathing, be sure to turn on kitchen and bathroom fans whenever doing something that has the potential to generate steam, like boiling a pot of water or running a steamy shower.
  3. Turn down the humidifier or turn on the dehumidifier.
    It’s tempting to automatically turn on the humidifier during a cool, dry winter. But before you reach for the dial, ask yourself if you really need to turn it on. You may find out you don’t even miss it!
    Reaching the right balance of humidity in your home can be challenging. The Centers for Disease Control and Prevention recommend keeping relative humidity levels between 30% - 60% to prevent mold growth. Keeping relative humidity levels between 30% and 40% during the cold winter months is optimal. Find the right balance between humidifiers and dehumidifiers to keep your home comfortable all winter long.  
  4. Turn on the ceiling fan.
    Circulating air reduces the formation of condensation. Reversing the direction or your home’s ceiling fan in winter (to rotate in a clockwise direction), will help keep air flowing in your home without cooling the air.
  5. Install weather stripping.
    Install weather stripping according to the manufacturer’s instructions for all offending windows.
  6. Rearrange.
    Have you recently moved an enormous collection of potted plants indoors? Do you keep your fish tank near a window? Plants and open containers of water can feed wintertime window condensation. Consider moving plants, fish tanks and the like a few feet back from the window to reduce condensation on your windows.
  7. Install storm windows.
    Storm windows serve as an additional insulating barrier. Installing them can decrease the appearance of condensation on the inside of your windows, but it may create a new condensation problem between your home’s window and the storm window.
  8. Install seasonal window insulation.
    Plastic window film is a temporary, inexpensive weatherization product that can be installed on the interior of windows each winter. In general, insulating window film is seen as a suitable short-term solution when more expensive, more permanent solutions like window replacement or storm window installation are out of reach.
  9. Install curtains or drapes.
    Insulate the window with the installation of thermal curtains or drapes.

Between the Panes Condensation

Condensation between the panes of a double pane window or IGU is unsightly and usually means your window is not as efficient as it could be. The insulating properties of IGUs come from their construction. The pocket of air held between the two panes creates an insulating layer between the interior and exterior pane. If moisture condenses on the inside of an IGU, it means the seal or glass has been compromised.

Mending double pane windows can be tricky business. Here are some of the ways our technicians help homeowners find success in repairing double pane windows:

  • Replacing a single pane of a double pane window.
  • Repairing cracked or broken double pane window glass.
  • Replacing old or weathered window seals.

The only way to truly mend the foggy interior of a double pane window is to replace the double pane glass or sometimes, the whole window. Each of the methods described above is a stopgap measure that will help buy time before investing in a new insulated glass unit.

Need Help with Foggy Windows?

Don’t let foggy windows dampen your spirits. At Glass Doctor we specialize in window repair and installation designed to keep you seeing clearly year-round. Contact your local Glass Doctor  or schedule an appointment online to learn more about how to reduce winter window condensation in your home.

Thinking about installing a dehumidifier to reduce the interior condensation in your home? Learn everything you need to know about dehumidifiers from the HVAC experts at Aire Serv. Like Glass Doctor, Aire Serv is part of the Neighborly family of trusted home service professionals.