You should replace them regularly, approximately every 30 days. Newer systems typically use pleated filters, also rectangular filters with a depth of approximately one inch. If you don't have allergies, you should replace them approximately every 90 days, but air conditioning professionals usually recommend them every 45 days for maximum efficiency. The only way to be sure how often the air filter needs to be changed is to perform a visual inspection of the filter every month.
After a few months, you'll get an idea of how quickly it gets dirty. You'll need to re-evaluate if you're having a new pet or if the outside air quality has been poor. More cycles mean more passes through the filter and opportunities to trap contaminants, so filters tend to fill up faster during periods of heavy use. As a general rule, lower home occupancy extends the life of an air cleaner, while higher home occupancy reduces it.
If your dirty air filter is completely covered with dust and dirt, it's a good idea to replace it even if it hasn't reached the end of its recommended lifespan. For every dog that has a shed of hair, expect to replace the filter a month earlier than you would with a pet-free home. And in doing so, the HVAC air filter will work twice as hard to overcome these barriers, making the unit less energy efficient. If there are no smokers or pets in your house, and your filter is the best-selling 1-filter filter with a MERV rating of 4, you should be able to wait up to 90 days before changing it.
During the mild spring and autumn, the air conditioning system will operate less frequently, so the filter won't get dirty as quickly. These general guidelines do not consider the sizes or types of filters, such as coarser filters or smaller filters. However, it's easy for busy people to overlook this task, and some may find that it takes several months before they remember to replace their air conditioning filter. The air conditioning filter protects the internal mechanics of your air conditioning system so that it doesn't build up with all those dead skin cells.
Whether it's oven filters, air filters, or any other part of the unit, be sure to take care of your HVAC system to extend its lifespan. As a general rule, it is recommended to change HVAC equipment (we are talking about filter filters, air filters, oven filters, etc.) And, if you buy an older system, plan to replace the filter more frequently to maintain filter quality.