I may be in the minority here, however the only time I go out and buy air filters for my central heating and air conditioning plan is when they are on sale, but what I will do is wait till there is a sale someplace on the air filters that I use for my central heating and cooling unit, and then I will buy a ton of them in bulk amounts to last me for many months, this ends up saving me a lot of money in the long run, it is kind of silly I know! But it is a system that has been working for me for a long time, so as long as there are still sales on air filters for my central heating and air conditioning plan every few months or so, I will continue to do this system of things! Of course, if it does not work out that way and I begin noticing that there are not as multiple sales going on with air filters for my central heating and a/c, then I will have to go and just start buying air filters as needed mostly almost everyone else does, then how did all this begin? Well I could not actually tell you to be totally honest. I just know that one day I came up with this system to only buy air filters for my central heating and air conditioning plan when they are on sale and buy them in bulk at that time. I have been doing this for at least 3 years now and so far it works out great.