Why Do Windows Get Foggy?

To get to the heart of this matter, we have to dive into just a bit of science. When you see a window that looks “foggy”, what you are seeing is condensation. Moisture condenses on the surface of the glass, developing a layer of water and clouding up some or all of the window pane.

Condensation occurs when warm, humid air comes into contact with a cold surface like the glass of your windows. Warm air can hold more moisture than cold air, and it will leave some moisture on the surface of something cold – and your window glass is likely to be some of the coldest places in your home.

Where is the Condensation on your Window?

Condensation on the inside pane of the Window

If you have warm, humid air and cold outdoor temperatures inside your house, foggy windows are a possible outcome. In many cases, this doesn’t mean anything is wrong with your windows. It can just be a matter of the conditions that are in place in and around the house. With that said, something may be wrong with the windows, so it’s a good idea to look a little closer.

Condensation on the outside pane of the Window

The above is true during the winter months when warm, humid air inside of your home comes in contact with the cold glass of your window. The opposite effect is true in the summer when warm, humid air outside your home comes in contact with the air-conditioned, cooled-down glass of your windows, which, under the right conditions, will cause condensation to form on the outside pane of glass. This is also not a concern and you can expect this to clear up shortly after the daytime sun reaches your window.

Condensation on the in between the panes of the Window

A double-pane window has a seal that holds air between the two panes. This is a modern design that allows windows to insulate far better than the single-pane windows of the past. When homeowners see a foggy window, they often assume that the moisture is between the panes and that the seal has broken to allow moisture to get in where only air is supposed to be.

If the moisture is, in fact, between the window panes, the seal has likely broken, and the window may need to be replaced. But it’s not wise to jump to that conclusion. It’s possible that the condensation could be on the inside or outside of the window, rather than between the panes, meaning that the seal should still be intact.

Quick Test to Check Window Condensation

Before you get too deep into analyzing this situation, you can look at one thing to determine if this is likely a seal issue or just a matter of humidity and temperature. Is more than one window fogged up in your home? If you are seeing this problem across multiple windows, it’s highly unlikely that seals are to blame. The chances that the seals in all of those different windows have failed are very low, and you are almost certainly looking at weather conditions as the cause of the fog.