Dirty filter has tremandous impact on the air quality inside the house and the integrity of the furnace and air conditioner system.
There are so many factors affecting the frequecy of filter replacement such as the quality of the air indoor and outdoor, the settings of the furnace or air conditioner (frequency of the equipments running), the quality of the filter use and etc. Service Express recommand to check filter periodically (recommanded every month) to ensure the filter is in good condition.