Well, how often you get your furnace maintained and serviced all depends on how often you use it. We rarely have harsh winters in San Diego, so once a year is probably sufficient, but if you tend to run your heater during the fall and winter months, twice a year would be more sufficient. If you use your air conditioner or heater, you should be changing out the filters every 2 to 3 months. This is to ensure you’re getting proper airflow and cleaner air.