Quick answer: Most manufacturers recommend air filters be changed once a month.
Why? …Clean Air Conditioning units run more efficiently. Units running with dirty filters or no filter will eventually plug up (and run less efficient!) … plugged units will eventually require cleaning that will possibly cost hundreds of dollars to clean.
Consider this: changing your filter every week for a year would likely cost less than paying for a single coil cleaning… not to mention the added cost of running a less efficient (dirty) Heating/Cooling unit.
At TRS Air Conditioning Services and Construction, Inc. we recommend you keep your filter clean, in fact a filter check is one of the things on our maintenance ESA checklist. For many, this means changing the filter monthly, but for some this means that the filter can go longer and in a few cases monthly is not often enough. If the filter is very dirty when you change it, shorten the interval between filter changes. During the summer, likely the filter will need to be changed sooner.
Some factors that affect how often changing the filter is needed:
Pets – If you have pets, keep in mind that the Heater/Cooling unit will draw in the loose hair that your pet sheds and the filter will capture it. With pets in the house, you will need to change your filter more often.
Allergies – When you or others in the home have allergies, more often air filter changes will be better.
How often the equipment runs each day – The amount of time your Heating/Cooling unit runs is a big factor in how quickly the filter needs to be changed. During the Summer the Air Conditioning is on more than the Spring and Fall and so the filter will need to be changed sooner. During mild weather with less run time of the equipment, the filter will last longer.
Filter size or quantity – Some homes have more than one filter or a very large one. By increasing the total surface area of filtering material, the amount of contaminants that can be captured is also increased. Usually this will result in the filter(s) lasting longer.
In short – change your air filter often… filter changes are the single most important maintenance item on your Heating/Cooling unit and you can do it yourself.