How do you stop house windows from fogging?

Each area of the country has different climate problems, but as a "rule of thumb" fogging is caused by the moisture level in your home, reducing your humidifier level should help, but the level of humidity helps you feel warm in the colder months so don't reduce the level too much. Your humidistat will have suggested levels for the average temperature outside. These are estimates and takes a little trial and error for your particular home. Hint: your humidistat (if your furnace is equipped) will be located very close to the furnace, usually attached to one of the ducts.