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Nominal Vs. Actual Sizes: Finding the Right Air Filter Size

Buying the Correct Size Air Filter- The Most Important Thing to Know 

When you are buying your air filter online most important thing to know is Air Filters have two sizes that you need to understand the Nominal size(which is a round size often used to label the filter) and the Actual Size. Not understanding these numbers often leads to consumers purchasing a filter that does not fit their Furnace or HVAC system. See the complete list of Air Filters by Size Rating and Brand.

Nominal vs Actual air filter size by Atomic

For instance a 20x30x1 may be on the label of your filter, but if you measure the filter you will see the actual size is less than 20x30x1 Air Filter Nominal Size. It may be 19.75x29.75x.75 actual size.  

Understanding Nominal Filters Size Could Save You Time and Money

Not understanding the Nominal Filter Size is the primary culprit for incorrectly purchased filters. The Nominal Size is the usually the dimensions used to Label the filter. For instance 16x20x1. These dimensions are a rounded value on the filters actual measurements. The actual measurements on this filter may be 15.5x19.5x.75, but that could vary by brand and manufacturer. So in order to make sure you have the correct size filter, especially if you are replacing with a different brand it is important to confirm the actual size on the filter. When purchasing filters on the internet the Nominal size is usually found in the product title.

Actual Filter Size- The Key to Making the Right Replacement Filter Purchase

The actual size as you might have guessed are the actual dimensions of the filter by length, width and thickness. This size is often on the filter right below the Nominal size and is usually labeled as the actual size. When you are buying a filter online the actual size is sometime in the product bullet point or the product description. If your filter does not have actual dimensions on the outside of the filter, you can measure you filter to get the correct dimensions. Some brands have a foam gasket on the outside of the filter, in this case, you will want to make sure you have a compatible actual size and that it also has the foam to ensure a snug fit. 

Lennox Air Filter X0851 with Foam strips

Examples of Nominal and Actual Sizes

 Size  Example 1  Example 2
Nominal Size 20x20x1 16x20x1
Actual Size 19.5x19.5x.75 15.75x19.75x.75

 

 Furnace filters should fit securely but should not have to be forced into position. If you have to force the filter into its slot, then it is probably too big. Forcing an improper filter size in a filter can cause it to buckle, damaging the filter or reducing its ability to function properly. Filters are a smaller than their slot to allow for easy replacement. Some HVAC units may need a filter with dimensions that are unique or uncommon. In these cases, a custom filter needs to be ordered.

AC Filter Sizes: How to Find the Right Replacement Filter

Find Your Filter Sizes Easy in 1" Deep Filters , 2" Deep Filters, 4" Deep Filters

Related Links

Furnace Filters

Best Place to Buy Air Filters Online

16x25x1 Air Filter

16x20x1 Air Filter

20x20x1 Air Filter

20x25x1 Air Filters

Lennox Air Filters by Size and Model Number

Lennox X6672 HCF16-16 Healthy Climate 16x25x5 Merv 16 Filter

Nominal VS Actual Size: Find the Right Furnace Filter Sizes

How to Choose The Right Home Air Filter Everytime

Buy a Replacement Air Purifier

Atomic Has Been Privileged to Support

Atomic Has Been Privileged to Support

Founded by the the son of a US Navy veteran, Atomic Filters has been proud to support the following Charities that support our veterans and their families.

Atomic Filters has supported Special Operation Warrior Foundation, UDT Seal Foundation and Fold of Honor.

Founded by the the son of a US Navy veteran, Atomic Filters has been proud to support the following Charities that support our veterans and their families.

Atomic Filters has supported Special Operation Warrior Foundation, UDT Seal Foundation and Fold of Honor.

Based on 3737 reviews
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Very Pleased

My filters were delivered quickly and the price was competitive. Good work!

Fast Response

Great service. Received my order on time.

Finally, a more reasonable price!

The standard price for these particular filters has obviously been a rip off by many places that sell them. One need only compare their size, that is the amount of material needed to make them, with other sizes that are similar and sell for a much lower price.
Atomic filters has always had the best price, but their new brand of the identical sized filter being much lower is a relief. Thank you for providing that. Perhaps if lots of people buy them the price can be lowered even more to what I would guess would provide a fair profit for everyone.

Solid replacement filters - TopTech TechPure TT-FM-1620 OEM (16x20x4)

Received the filters quickly. Excellent price. They fit perfectly in our heat pump filter rack. The only thing I wish is that TopTech would offer a MERV 13 filter for even cleaner air.

Outstanding service.

Excellent product as advertised ... Prompt efficient service and communication

Fixed my issue.

Both of my uv lights burned out at the same time. I replaced them and they still did not work. Next step was replacing the ballast. Super easy to do it. Lights working again.

Saved money

Arrived when promised, exactly the right product, and delivered to my door for less than i had been paying for the filter.

Great cust serv. off brand filter so so

Atomic Filters customer service is top notch. Tried Carrier knock-off brand. one worked one did not in a carrier Air purifier.IE the bad filter caused an error code. Atomic paid return ship and sent new carrier brand replacement which was nice.

Great Service

Atomic Filters is great. Very much appreciate being able get the filters needed at a good price and so quickly. And customer support was great when an incorrect size (that I ordered) needed to be returned. A new customer for life here!

Perfect fit, Excellent service!!

The filter is an exact fit for my Carrier Infinity system. Customer service is top notch and shipping is fast. Atomic is my go-to place.

As good as expected, better than anticipated.

As good in construction as the more expensive filters that I bought for years, and the Atomic Filter cost less also.

Fit perfect, didn't have to change anything or do anything different. It is now performing it's duty.

Very nice filters. Definitely will be ordering these again instead of the 3M Ive used for the last 18 years . Like these are really well made. And price is on point. And very quick delivery.

Air filters merv16

They don’t come much better then these and are great value as well

Cleaner Air, Better Price

Judging by the price, original equipment HVAC manufacturers are quite proud of the filters they sell. My guess is that most don't manufacture filters and buy them from outside suppliers. In my experience, Atomic filters provide the same level of filtration and considerably lower cost than those sold by the companies that manufacture heating and air conditioning units.

Phenomenal! So Impressed

I ordered direct from Atomic Filters instead of ordering on Amazon. I can’t tell you how great this company is. Not only was the product cheaper on Atomic Filters, but the shipping was super fast. I 100% recommend Atomic Filters. Great company!

Same quality slightly better price...

Keep competitive in your pricing and you'll continue to get my business.

Will re-order every year as needed. Good service from the company.

We have been pleased with these filters and will continue to reorder as needed.

Great all around find.

I’ve lookied for these HEPA filters from several sources.
Atomic filters had the exact match, great price and they arrived quickly.
Will definitely order again

Perfect

Love the filter. Perfect size. Love the company more. Have bought several times from them since this filter is hard to find. This time the filter came in and FedEx had crushed it in delivery. Called CSR service and sent them a picture of the crushed box and they immediately sent me out another one which arrived in great shape. Will continue to buy from Atomic Filters because of their great product and great customer service!

Love it

Received my filters in excellent condition. The price for the two filter package saves me money. They were shipped quickly, and I have a reminder with the company to ship on a timely basis! Great company to work with.

HEPA filter

Fits good. Fast delivery..mail buy from again..

Filter replacement

Replace my original equipment filters with atomic house, brand filters.
Filters are very good quality, same fit size style and function. Would definitely recommend these filters as replacements.

Great customer service

Great customer service , however shipping was slow to get to me

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