Check the humidity level inside each room where you notice the fogging and condensation. Frost, fog and condensation on the windows are often caused by high levels of humidity in the air. The easiest way to tell if humidity levels are to blame is to compare the humidity levels in a room where the windows need to be defrosted to a room where the windows remain clear. You can purchase a simple humidity gauge at a hardware store.
Install a dehumidifier in each room where the windows need to be defrosted. Place the dehumidifier as close to the window as possible to get the best results. Reducing the amount of humidity in the air should help to eliminate any problems with condensation on the windows in your home.
Open and close the windows firmly to ensure that they are closing properly and that there is no gap between the window and the frame. A gap between the window and the frame lets cold air in and helps to create a frost and fog on the windows. If any of your windows have gaps, they should be repaired as soon as possible. Repairing defective windows should eliminate the frost and fog problem, and it can also save you money on your heating and air conditioning bills.