When it comes to air filters, most manufacturers and HVAC companies recommend changing them every 90 days or 3 months. This may vary depending on the location of your home, if you have pets, and the age of your system and equipment. As a general rule of thumb, it's best to keep track of how long the air filter has been in place. For cars, the average length of service is usually 10,000 to 15,000 miles, which is approximately once a year.
However, this is just a recommendation and doesn't take into account your individual driving situation. If you can't tell by looking, but it's been more than three years or 30,000 miles, it's probably time to buy a new one (especially if you can save money doing it yourself). In most cases, drivers should expect to spend more than a year and probably more than two years between air filter changes, depending on conditions and mileage. Stop-and-start driving places more demands on your car and will also make your air filter dirty faster.
To know for sure how often to change your engine air filter, consult the maintenance section of the owner's manual or Google the manufacturer's recommended service interval. The purpose of the engine air filter is to prevent dust, dirt, and other environmental contaminants from entering the engine. For home air filters and heating filters, they should be replaced every 90 days. However, if you have a smaller appliance used for cooling, you may need to change the filter more often due to its smaller size.
To locate the engine air cleaner housing, look for a large plastic housing that sits above or to one side of the engine. When you remove the air filter from the air handling unit, if you hold it close to a light source, you can see if it's dirty or clogged; if you can't see the light through the filter, it's time to change it. To keep air quality under control and your home clean, you'll want to replace the filter with a minimum interval of 2 to 3 months. If someone in your family suffers from mild to moderate allergies, you can put on a better air filter or change it more often.
Driving in dusty or rural locations can also cause air filter performance to decline more rapidly.