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Lennox Furnace Filters

Lennox X0586 20x25x5 MERV 11 Box Replacement Filter - 2 Pack

Size Guide

The Lennox X0586 Healthy Climate boxed media air cleaner has MERV 11 filtration and removes up to 85% of particles such as dust, dirt, and mold spores down to 3 microns and have no ozone emissions a known lung irritant. This is an excellent filter for someone who wants a significant upgrade over standard fiberglass filters from the hardware store.
  • 2 Pack
  • Filter Rating: MERV 11
  • Nominal Size: 20" x 25" x 5"
  • Actual Size:  20" x 24.75" x 4.375"
  • Expected Duration: 6 to 12 months
  • Fits the following filter models: BMAC-20C, Honeywell F25F1026, Honeywell F35F1016, Honeywell F50A1009, Honeywell F50A1108, Honeywell F50E1067, Honeywell F50F1065, Honeywell F100B1032, Honeywell F100F1038, Honeywell F100F1087, Honeywell F100F2010, Honeywell F100F2044, Honeywell F100F2051, Honeywell, F150E1034.FC100A-1037 & FC200E-1037

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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 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


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.

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