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For general information about central air systems and filters, see this article Central Air Systems & Filters.
Firstly, an air filter's primary purpose is to protect the equipment in your central air system. Basic filters will trap larger particles from building up on the fan or heating/cooling elements. This central equipment was (hopefully) designed with the size of your home in mind, which means it should provide the adequate ventilation needed for your home if maintained properly. One critical element of this system's performance is the air pressure.
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