How often should I change my air filter?
It depends on the type of air filter you have. If you have a one-inch-deep pleated air filter the rule of thumb is every three months. On the other hand, if you have a five-inch-deep pleated air filter the rule of thumb is every six months. A cheap throw-away fiberglass filter should be changed every month. Fiberglass filters do not clean the air in your home very effectively. These throw-away fiberglass filter are designed to protect the blower by trapping larger dust particles and insects, like roaches, spiders, and other insects.
As stated, the above time frames are rules of thumb and rules of thumbs only work sometimes. So, here is the true answer. The only way to know when to change your air filter is to look at it every so often. This is because there are many things that come into play. If you live in a dirt road your filter may need to be changed more often. Other factors are: If you run your blower often, if there is construction in your neighborhood or in your home, if there is a mild winter and your system does not run much, etc.
So, the only way to know is to pull out that air filter and take a look. If there is hardly any air coming out of the registers, you waited too long, and your system may get damaged. One last thing, there are gauges you can install that sense the air pressure and can alert you when it is time to change the air filter. However, the gauges that work really good can be quite expensive. There are some inexpensive gauges but we tested a few and I would only give those gauges three stars, at most.