Double pane windows can be tough to clean. They have the tendency to fog up between the window panes and at times they might seem impossible to defog. However, they can be cleaned and defogged easily enough without replacing any windows.
Here is how you can defog them yourself.
You should begin by being prepared not to allow kids or pets into the room or area with the window you need to defog. If it is in another room, just leave the door closed and with a note on it. If it is in the kitchen or living room, clearly mark off the area with masking tape on the floor.
Make sure you have all supplies handy and nearby.
You can start drilling in the upper corner of the window. Make sure that you have a small hole that will be big enough to air out the window. After you do that, drill another small hole in the corner of the lower half of the window that is diagonal from the first hole.
Sweep and Wait
Sweep away any glass bits that may have fallen onto the floors or surrounding area while drilling. Then wait for the window to clear up completely. This could take a few hours to a day or two depending on temperature, weather, and humidity.
Once the window has cleared up, you can tape the holes and using the needle to poke tiny holes onto the tape so the moisture can escape. Or you can leave the holes uncovered. Either way will work in preventing the windows from fogging up again.