I am NOT a HVAC professional, just a home owner consumer. Bought their 16″x25″x4″ filters for my house, which they sell in boxes of 6, in August 2019; installed right away. Did notice that it went in much easier than I’m used to in my other house. | Had my HVAC contractor who installed the system back today for a checkup. He pointed out that the filter is vastly undersized, so that it does not sit properly in place in the duct; so that there is a huge amount of air leaking around the edges – filter does not even stand straight (too short to catch on the retaining ridges), is angled, which increases even more the open space above the filter for dirty air to bypass and leak past the filter. Of the 12 filters I bought ($161.65 with 5% discount coupon applied), still have 9 un-used today. | Looked at the filter: while the label says nominal size is 16″x25″x4″, actual size is 15.5″x24.5″x3.75″. My contractor installed a Honeywell HVAC system, using Honeywell filters; which he says need exact 16″x25″x4″ dimensions. | Went back on the web site right away: reports that I have NO previous orders. Called customer service: they said their current customer database does not reflect such “old” purchase history. | They said I only had 30 days to file for returns, so I’m now stuck with 9-10 filters, which I’m probably going to have to discard and buy a proper set of filters instead. | They are probably legally covered by all the fine print and disclosures, so I’m actually stuck. | Reporting this case to show that they are not interested in assisting or caring for customers: once you bought it (with no responsive customer help to help you choose what you need), you’re on your own. They won’t lose any money from refunding or exchanging merchandise from me, but they won’t get a penny more purchase from me either. If you are considering buying from them for their cheap filter prices – make up your own decision on whether buying from them is the right thing for you; given my experience that after the sale, your custom is worth nothing to this company.