You can wipe condensation off the inside of a window. You cannot wipe fog off the space between two panes of glass. If you are seeing a haze, drops, or a milky film inside a double-pane window, that is a different problem, and it is worth understanding before winter gets going.
Three kinds of window moisture, and only one is a seal problem
On the inside surface of the glass: indoor humidity meeting cold glass. It wipes away.
On the outside surface of the glass: dew from outdoor conditions. It is normal and wipes away.
Between the two panes: the sealed unit has failed and moisture has gotten in.
If you are not sure which one you have, try wiping it. If it does not move, it is inside the unit. Our post on condensation covers the other two in more detail.
What a double-pane window is supposed to do
A double-pane unit has two layers of glass with a sealed space between them. That sealed space is a big part of how the window insulates. When the seal is intact, the space stays dry and clear.
Why seals fail
Age. The materials that seal the edges of the glass wear out over time.
Temperature swings. Western PA and Eastern Ohio winters mean repeated cold and warm cycles, and the glass and frame expand and contract each time.
Moisture and pressure changes. Over time, small gaps can let humid air in.
Installation or frame issues. A window that sits in the opening poorly can stress the unit.
Is it a problem?
It is not a safety issue. It does mean the unit is no longer insulating the way it was designed to, and the fog tends to spread and stay. It is also one of the clearest signs a window is nearing the end of its life. It sits near the top of our list of five signs your windows are past their lifespan.
Your options
Replace the glass unit. If the frame is in good shape, only the sealed glass may need replacing.
Replace the window. If the frame is warped, drafty, or the window has other problems, replacing the whole window is usually the better long-term fix.
Live with it. Some homeowners do, especially if it is one window. It will not go away on its own.
Ask any contractor to explain why they recommend one over the other, and get the warranty on the work in writing.
Frequently asked questions
Can foggy windows be fixed without replacing the glass?
Some services drill and vent the sealed unit to clear the fog. Results vary, and the original seal is not restored. Most of the time, the lasting fix is replacing the unit or the window.
Does one foggy window mean the others will follow?
Not always, but windows installed at the same time have aged under the same conditions. It is worth checking the others.
How much does it cost to fix a foggy window?
It depends on whether you replace the glass unit or the whole window, and on the size and style. We do not give a figure without seeing the window. A free estimate starts with someone looking at it.
Find out which option fits
If you have fog between the panes, schedule a free estimate. We will tell you whether the glass or the window needs attention, and why. You can see our replacement windows on the windows page.
