Fogged windows can be a real… nuisance (no bad puns today). Fogged glass makes windows look constantly dirty, and some windows get so cloudy that you can't even see through them. These windows will also have a lower insulating value, but not by much. While replacing the window is usually most people's first instinct, this isn't always the best approach. A couple other options would to replace just the pane or have the window serviced to make it look clean again.
Replace The Pane
Rather than replacing the entire window, you can replace just the defective pane. Most newer double-hung windows have sashes that can be easily removed without any tools. Major manufacturers such as Pella, Anderson, and Marvin all have 20 year warranties on their glass. If a window less than 20 years old develops foggy glass, contact the manufacturer. If the window is older than 20 years, you can still replace the pane for less money than it would cost to rip out and replace the window, but you'll need a window specialist to do the work.
Service The Pane
Some window repair companies, such as Window Medics, will repair alter windows with broken seals to make them look good again. This process consists of drilling a couple tiny holes in the glass, washing out the inside of the window panes to clean up the 'fogginess', and then installing tiny vents in the holes to allow the window to breath. The window will no longer be foggy, and it will stay clean. The downside to this repair is that the window will have a slightly lower insulating value than it had before the glass fogged over, but this will cost much less than replacing the window.
Reuben Saltzman, Structure Tech Home Inspections - Email - Home Inspector Saint Paul
