The HVAC company said 4" filters have more surface area and therefore last longer and do a better job of filtering than the 1" o Got a new HVAC system installed about two years ago. The HVAC company said 4" filters have more surface area and therefore last longer and do a better job of filtering than the 1" ones. There's more surface area, so that makes sense. Unfortunately, they made the opening so it would only fit a Top Tech brand which are pricey. I tried other brands from Home Depot, Lowes, etc., but they were all a little too big in one or two dimensions. Finally came across Nordic Pure and it fits perfectly. Whatever you buy, carefully measure the dimensions of the opening and the existing filter then check the ACTUAL dimensions of the filter you're planning to purchase if you want to try a different brand.The air filter opening is simply sheet metal, so if you have a 1" filter and want to switch to a 4", I don't imagine it would cost terribly much to pay an HVAC or sheet metal company to redo the filter opening. Just a random thought. 5 FALSE ADVERTISING In the fine print "Actual Size of Filter: 19-1/2 x 24-1/2 x 3-5/8". Why does it read 20x25x4? It should not have that as it's advertised size. I've been buying filters for this furnace for years. It does not fit. It should be the 20x25x4 that it says not a different dimension in the fine print. 1 Works Great! Just Measure First!! Fits and works well; much better than the OE one that came with the system. Don't believe all the bad reviews (Filters in general get a lot of bad reviews due to people ordering based on the Nominal Size.... a 2x4 isn't really 2"x 4" people ;-) ...). BEFORE YOU ORDER; take a few minutes and make note of the Actual Size of your old filter (should be printed on the side and they ALL vary depending on manufacturer) then measure the filter opening of your system (For example; my system could take a slightly larger filter than what it came with). LAST: Read the description on Amazon for the actual size, double check, order then enjoy your clean air! 5 The best filter, hands down! I bought these for an air purifier I am going to make for my townhouse. I have made a few different designs over the last few years, and have done experiments to see what design works the best. My design uses two HVAC filters. I have tried many different filters, and while they worked OK, I never found a filter that worked as I thought they should. I did find some online that claimed they were Merv 13, but they were more like Merv 8 and we're very poor quality.However, i finally found these Nordic Pure Merv 15 filters, and they are awesome! I am so pleased to finally find a filter that performs to fit my needs. I have tested these filters and can tell you that they are Merv 15, and the best HVAC filter you will find for the price; trust me, I've looked. Not only do they filter better than any filter I've tried, they are also the same price as any store bought Merv 12 filter!The filter is not a true 20x25. This is normal for aftermarket filters. It's smaller to filt different HVAC units. OE filters are usually an exact 20x25. The build quality of the filter is better than other aftermarket filters I've tried. You should note that this is not the same build type as some highend merv 15-16 filters. High-end Merv 15-16 filters are much higher quality to meet hospital regulations and requirements, and are much more expensive.Nordic Pure is an American company, and their filters are made in the USA. If you are looking for a quality aftermarket HVAC filter, I highly recommend Nordic Pure 5 The sizing is NOT correct Ignore the 20x25x4 - it's just a dumb name that means NOTHINGThe filter is WAY smaller than that - I had to tape sheetrock to it to get it to fit and even still - it's only 3" thick (not 4") 1 Good product, good value, I'll buy more in the future This is the second time i've ordered the Nordic Pure filters. They work well, helping to clean the air and are reasonably efficient for their HEPA 18 rating (Higher HEPA rating means more resistance to the air flowing through it, so you need a a balance).The price is good and in lesser parts of the house where we don't run the HVAC as often, they last much longer. Further, in an instance where one wasn't replaced (accidently) for 6 months, it still passed air and worked well with a coating of dust on the cleaner material. Yea, I'll order these again.This is a real review, generated by a human, that actually bought these from Amazon twice now. 4 A MERV rating of 9 to 12 will stop particles in the 1 - 3 micron range. A great choice for homeowners for best dust control. Great product. We have been using this brand of filters in our furnace for 4 years, we change them out every 6 months.MERV, or Minimum Efficiency Reporting Value, is a numerical value given to filters in order to identify its filtering abilities.This is now an international industry standard. This standard is used for determining the filters ability to capture and hold dirt and dust in specific size ranges.A MERV rating of 12 means that Average Particle Size Efficiency in Microns is 1.0-3.0 80%-89.9%, 3.0-10.0 90% or greater. Filters with a MERV rating of 9 to 12 are used in commercial and industrial applications and will stop particles in the 1 to 3 micron range. These filters are a great choice for homeowners who want the best dust control possible.I seldom have to dust. I think that this is a very good MERV rating for most households and getting a filter with a higher rating would be as waste of money as our filters rarely look used when we change them out.I 5 Don't buy this! There was only one filter delivered in the box. Over $90 for one filter???? False advertising! It was advertised as a 6 pack. 1