The only way to be sure how often your air filter should be changed is to visually inspect it every month. After a few months, you'll get an idea of how quickly it gets dirty and need to re-evaluate if you have a new pet or if the outdoor air quality has been poor. The basic consensus among HVAC professionals is that you should replace your furnace filter every 90 days or every three months. However, that depends on the thickness of the filter.
Thicker filters have more room to accumulate dirt and dust, so you don't need to change them as often. Thomas & Galbraith Heating, Cooling and Plumbing, of Ohio, recommends changing filters less than 2 inches thick every 30 to 90 days. Three- or 4-inch filters can last 6 to 9 months, and filters up to 6 inches thick can be replaced once a year. In general, fiberglass air filters should be changed about once every 30 days or as recommended by the manufacturer.
Pleated air filters should be replaced approximately every three to six months. However, the frequency of air filter replacement depends on several important factors such as your home, occupants, and location. If you have one or more pets, consider replacing a fiberglass air filter about once every 20 days and replacing a pleated air filter about once every 60 days. Any use will cause a certain amount of dirt to be trapped in the air filter; after all, that is its function.
What might be an appropriate air filter replacement frequency for one home may not be the right choice for every home. After a period of smoke-filled days and poor outdoor air quality, inspect the air filter to see if it needs to be changed. If furniture is filled with dust soon after cleaning the house, the oven filter may be clogged and can no longer effectively remove dust from the air. On average, you should change a fiberglass air filter about once every 30 days, while you can leave a pleated air filter for three to six months before having to replace it.
As a general rule, lower home occupancy extends the life of the air filter, while higher home occupancy reduces it. Wait up to three months to change a fiberglass air filter and nine to 12 months before changing a pleated air filter. However, people in the north whose ovens are not interrupted for months may prefer to change the filter every 30 or 60 days, since more air passes through the filter and it clogs up more quickly. The filters are designed to trap dust and particulates suspended in the air as the air passes through the filter and into the furnace system.
The HVAC air filter helps keep indoor air clean by trapping particles of mold, pollen, and other pollutants that move through the system. When the filter becomes clogged with dirt and debris, air cannot pass through the filter properly. In general, if you have to vacuum or sweep more often than usual, you'll probably need to change your air filter more often as well. Air filters are designed to allow air to flow freely through them while at the same time trapping dust, dirt, bacteria, and other contaminants.
