The only way to determine how often you need to replace your air filter is to inspect it every month. After a few months, you'll get an idea of how quickly it gets dirty. You'll need to reassess if you have a new pet or if the outdoor air quality has been poor. The ideal is to change your air filter every three months, however, there are certain factors to consider when determining when to change an old filter.
A general rule of thumb for pleated air filters (such as those manufactured by FilterBuy) is to replace the filter every 90 days. As the filter traps more dirt, dust and allergens from the air, the efficiency of the filter decreases. In smaller homes, the HVAC system has to move less air, which can mean less frequent air filter replacements. Marking your calendar every 90 days or trying to remember the last time you changed your filter can be a challenge, which is why many oven manufacturers recommend replacing it at the beginning of each new season.
A professional will be able to help you if there is a particular protocol for changing the air filter of a specific brand or how often an air filter needs to be changed. Typical recommendations range from every 30 days for cheaper fiberglass filters (which often don't do a good job of filtering), to 6 months for high-end pleated filters. Whether it's oven filters, air filters, or any other part of your unit, be sure to take care of your HVAC system to extend its life. Depending on your lifestyle and the type of oven filter you choose, you may want to change it more often. The short answer is that, according to most air filter manufacturers and HVAC companies, you should change your air filter every 30 days when using less expensive fiberglass filters.
Filters receive a minimum efficiency report value (MERV), ranging from 1 to 16, although ratings 6 to 12 are best for residential furnaces. However, these appliances are often built with smaller filters and, therefore, may need to be changed as often as a filter in a larger home. If someone in the household suffers from severe allergies, it is recommended to change air filters very often; in some cases, every two weeks. If you have an asthmatic or allergic person at home, change the filter every 6 weeks to ensure that the indoor air quality is the best. During mild spring and fall, your HVAC system will operate less frequently, so the filter won't get dirty as quickly. However, northerners whose ovens have no rest for months may want to change their filter every 30 to 60 days, because more air is being drawn through the filter and it will clog more quickly.