If you’re like more than 50% of your neighbors you wait the full 6 months… and frankly we understand – price is a concern. A good rule of thumb when purchasing new filters – don’t buy the cheapest and don’t buy the most expensive – a Merv 12 to 14 should do the trick and is our recommendation for 90 day replacement cycles. Plus the manufactures all agree – 90 to 180 days is about all you’ll want to extend the life of the filter out to. Even if it still “looks clean” it’s not. It’s filled with dust, dust mites, allergens and stuff you DON’T want floating around your home. Plus – your system is working overtime trying to pull air through the dirty filter… and that costs you money on your energy bills.