18x24x5 (17.75x23.75x4.38) MERV 10 Honeywell Grill Filter (2 Pack)

These are only available on Special order at Home Depot/Lowes and cost more money, I always buy 2, people will tell you they last 12 Months, I like to change them every 7/8, when they start to look dirty, so by buying 2, I always have over a years supply and Amazon always has the best price

These filters work in systems that use 18x24x1 filters, and have at least a foot of air space (5" for the filter plus 7" clearance). My air handler is above the filter space so I have about 3 feet of space, which is plenty. These filters have a lot more surface area and hold a lot more dust and debris than standard 1" filters, so the AC doesn't get overloaded from poor airflow. Plus you can keep them in for up to a year (Although I like to change mine out every 6 months). When I was using the premium 1" filtrete filters my AC handler wasn't getting enough air flow, if I didn't switch it every 30 days, so I would get too much moisture building up causing mildew to form. Now that I've switched, the air is clean and I don't need to worry about switching out the filter all the time. So even though they cost 4-5 times as much per filter, you get to keep them 6-12 times longer... a net win for sure.

PROS

+ 6-12 month life, less frequent changing

+ MERV 10 is about the best you can buy outside of a sealed system

+ Clean air

+ Great air flow

+ 5" of filter for 1" systems

+ Can be used in most systems that use 1" filters

+ Net savings over similarly efficient 1" filters

CONS

A little spendy up front

May be too easy to forget to change since you're not doing it as often

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