When I go to buy air filters for my central heating and air conditioning system unit I like to buy them in bulk.
And if I do not buy in bulk I like to buy at least 2 large packs.
The reason for this is to save myself headache, gas and time from having to keep coming back to the hardware store every single month. I change the air filter of my central heating and air conditioning system once a month even if it does not look or feel like it needs to be changed. This is a way to ensure that my central heating and air conditioning system is always working at the full power it was designed to. It also helps with keeping the air vents and the ductwork clean as well. I only get my ductwork to my central heating and air conditioning system cleaned once a year. Sometimes I may even skip it if it seems that there is no problem and the local heating and cooling specialist reports no issues when they do their usual heat and a/c tune up and check up every season. I think I am pretty much set in terms of air filters for my central heating and air conditioning system unt. I bought enough this last time to probably last me about a year or maybe even more! I also should mention that I buy washable air filters too, which extends the use of them. Washable air filters are pretty cool I have to tell you!