Q: How much will I save by changing the filter for my central air conditioner every month? What other benefits does it have?
A: The short answer is that it is unlikely that changing your filter every month will save enough to pay for new ones. The first thing to understand is that the purpose of the filter on your central cooling and heating system is to protect the coil from dirt and debris—leaves, twigs, gerbils, etc. It was not designed to improve the quality of the air in your house. The coil is where heat is exchanged, and if it gets dirty, it moves the heat less efficiently, so having a filter in place is important.
In extreme cases—either because the filter hasn’t been changed in a long time or because a lot of dust, fur, etc. is loading the filter—a dirty filter can slow down airflow and create enough pressure on the unit to seriously strain the motor and cause premature failure. Sometimes, the filter gets so clogged that it gets sucked into the unit, and air just goes around it, along with the dirt and debris.
The key is to find a balance: Change the filter often enough to prevent strain on the motor, but not more often than you need to, since that would be a waste of money. In most houses, changing it every few months will probably be about right; this should be often enough to prevent pressure buildup and damage. But pay attention to the filter. Inspect it after two months. If you can’t see through it, you need to change it more often. If it looks almost brand new, you can go longer.
If you want to improve your air quality by using the furnace/air conditioner filter to remove pollens, dust and other particles from the air in your house, you can get filters designed to do this. However, it is important to make sure the better filter won’t increase pressure on the system’s motor. One way to think about this is to picture a very dirty filter. There is so much dirt and debris on it that it becomes more “efficient” at collecting everything and will collect more particles than a “clean” filter. Eventually, it gets so clogged that the pressure builds up, slows down the airflow and strains the motor.
Similarly, a “high efficiency” filter will collect more particles but may also reduce airflow and put strain on the motor. Have a qualified technician certify that a more efficient filter won’t hurt your equipment.
Virtually every relevant website recommends changing the filter often and claims it will lead to energy savings, but it’s most important to learn what makes sense in your house.