After spending so many years in HVAC I can pass on some knowledge to my home inspection customers. We always told customers to use the cheap blue or white filters and spray pledge on them to catch the fine dust and change once a month.Why you ask should I choose to do this. Pretty simple actually with new pleated filters they are so restrictive that you lose a 1/2 ton of cooling as soon as you install them. Then after dirty that could drop to 1 or 1 1/2 tons making the unit work hard from day one and causing premature breakdowns and failures. Think of it like this home inspection customer, if you put a piece of cloth over a water hose it restricts the water flow. A pleated filter does the same cause it is basically a piece of cloth. These filters to me are not 3 months filters, I have had many units freeze up over them. We are talking about 1 inch pleated filters usually changed in the ceiling or wall. Even the pleated ones should be changed once a month especially if sized to small because a dirty filter sets a home inspector into oh oh they do not change filter mode. If you have a filter in the attic that is 5 or 6 inches wide these have much more surface area overall and will make a 3 month change out.Let us look at filter sizes old and new requirements.
old standards- 20×20 is 400 sq inches which you divide by 144 because the 144 sq inches in a sq foot. Doing this gives you 2.7 tons and this is a national standard so not just here in the Lafayette area.
So if you have a 24×24 filter it is good for exactly 4 tons the old airlow standards. You can do the math home inspection customers and see if your filter is big enough but this on older units or 14 seer and below.
New standards-they have increased the air flow static and velocity requirements. Let us take the same filter- 20×20 is 400 square inches but now you divide by 200 giving you 2 tons of airflow if the filter is clean. So a 24×24 now is 2.88 tons of airflow. New standards make a big difference with newer systems so please ensure you change your filter once a month and the right size is being installed.If you using 1 inch pleated filters is ok just change once a month.If you use pleated filters you want your returns in ceiling or wall over sized by 2 tons.So if you have 4 ton unit you want 6 ton of return. Thx my home inspector customers.