How often should I need to change my furnace/central air filter?

My furnace and central air share the same ducts. How often should I change the filter? (I use the 3M Filtrete brand).



The home inspector said once every 3 months, the guy who installed the central air said once a month.
How often should I need to change my furnace/central air filter?
The installer was correct. You need to replace the filter every month.



Air conditioning systems are very low pressure systems. That is, the air flow through the various ductwork has a very low driving force. For comparison, when you talk about pressure in a balloon, you are measuring in pounds per square inch.



In a household airconditioning system, you are talking about ounce of water pressure per square inch. This is a very small pressure drop, so dust accumlation on your filter will quickly reduce the flowrate. Two things can happen when the air filter is plugged....

The airflow across the cooling coils will become very low and the air will get very cold, causing water to drop out into the drain system. This can cause your drain system to become overwhelmed and you will get leakage out of the attic AC unit and onto your cieling.



The other thing is, it can overload your AC system and cause premature failure.



Buy the cheap whispy air filters 3 per pack and replace them every month. I use my yahoo calender to send me an email reminder automatically every month.
How often should I need to change my furnace/central air filter?
I tell my renters to change it monthly, if they use the heat and AC a lot, smoke or have pets. That being said, I don't use my HVAC unit at home much at all and even though I have pets, I check it monthly to see whether it has accumulated much, but most of the time, I wind up replacing it about every other month.
at every change of season.
once every 3 months
depends on how fast they get dirty. check them and see if they are dark and dingy, if so replace them, check them every month to see how fast they get dirty, if they don't look bad then check them again the next month, then you can decide for yourself on how much you need to change them per year.
Once a month unless it gets dirty sooner than that, but at least once a month. Especially if you have pets or you smoke in the house.
The last guy ALMOST had it right. The interval could be as short as 1 month or as long as 3 months. The only thing i disagree with him on is the 3 pack of whispy filters. They can potential come apart and the fibers can clog deep within the evaporator. I would use the 3m you have, make sure they are the paper pleated ones and plan on changing them on the first of the month. Keeping up with this will insure a long life for your cooling system.