In most applications Tim recommends using simple, disposable filters which are changed monthly. Although some people prefer thicker, pleated filters, they may find that the restriction of airflow gives them less cooling. Also, be diligent to change filters monthly. During the hottest months you may find your system works better if you change the filters every 2-3 weeks. If you have animals, you must be really watchful for dirty filters. Animal urine (carried in the air flow) will contribute to the corrosion of your a/c coil. Keep the kitty litter away from the a/c intake register. Consult your Tim’s A/C for the best advice on your specific system.