Back to the original question. Why are there so many different sizes? You may think like I did that it was a marketing ploy by the manufacturers to get you to have to buy the filters from them or your dealer directly but actually it comes down to the engineers.  The air conditioning manufacturers are mandated by the government to maintain certain standard energy efficiency ratings (SEER) for their air conditioning units much like the auto manufacturers must maintain certain mpg ratings for their automobiles. In order to do this and not violate certain patents of other manufacturers for what are pretty much the exact same general designs and operating systems one of the items that can be tweaked is the cabinet size. So while some manufacturers have indeed designed their systems to use a standard size filter like a 20”x20”x1” or a 16”x25”x1” many others have not been concerned with the plight of the residential home dweller. They have gone their own way forcing consumers to try and stuff standard sized filters into a non-standard opening. This creates a situation where the air escapes around the filter and clogs up the coil or an equally bad situation where air cannot make it easily through the filter creating high static pressure and eventually damages the fan motor, a costly repair. Fortunately now anyone can get the exact filters they need for an affordable price at www.mycleanaire.com and avoid damage to their air conditioner and stop wasting time and gas looking for them.

If it is to protect your equipment from particulates that can clog the coil in your air handler or furnace thus saving you from a costly service call to unclog and clean your indoor coil then a less efficient filter can be used.

Poly-synthetic filters or “rock-catchers” as they are sometimes coined can accomplish this goal and they will last longer between changing. I don’t like it when any company attempts to use “scare tactics” to sell their wares so I won’t do it now. All I will say is I am sure most people would prefer not to breathe in any more of the particulates in the air than they have to. With that said the simplest way to accomplish this is to use a more efficient air filter.

A pleated air filter is the most economic way to improve your Indoor Air Quality (IAQ). The pleated filter catches more particulates and thus has a faster buildup and will need to be changed more frequently. Another factor most people do not take into account is the amount of time your air handler/furnace is running. Both the winter and summer seasons of course see your system running the most and thus you will see more buildup. So it all comes down to this.

You really need to check your filter monthly for a long enough period of time to see how your lifestyle is affecting your particulate buildup. Some people will need to change every month, some every two months, and some every three months or longer.

Once you have established your frequency for each season you should be set until something changes.