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Water Filter Knowledge

Water Filter Standards

What should I look for when choosing a Water Filter?

Look for the NSF Standard Rating

NSF is an independent global health and safety organization.

What does NSF do?

Founded in 1944 as the National Sanitation Foundation, NSF International tests and certifies products and writes standards for the food, water and consumer goods industries. The name was changed to NSF International in 1990 as services were expanded worldwide.

1. NSF International is a global, independent, public health and safety organization with a mission to protect and improve human health.
2. Dedicated staff in North America, Europe and Asia to assist in product certification.
3. Over 200,000 square feet of laboratory space with one of the largest drinking water treatment unit test facilities with the ability to perform full chemical, microbiological and physical testing.

NSF/ANSI 42: Aesthetic Effects 

NSF/ANSI 42 is one of two main NSF standards for evaluating safety and integrity of residential water filters. NSF/ANSI 42 establishes the minimum requirements for the certification of POU/POE filtration systems designed to reduce specific aesthetic or non-health-related contaminants (chlorine, taste, odor and particulates) that
may be present in public or private drinking water.
The scope of this standard includes material safety, structural integrity and aesthetic, structural integrity and aesthetic claims. The most common reduction claims addressed by this standard are chlorine, chloramines, iron, manganese, hydrogen sulfide, pH neutralization and zinc reduction. In addition, products certified only as components are found under NSF/ANSI 42 and are evaluated for material safety and, if pressure bearing, structural integrity.

NSF/ANSI 53: Health Effects


NSF/ANSI 53 is the second NSF benchmark standard which addresses reduction claims for residential water filters. Standard 53 establishes the minimum requirements for the certification of POU/POE filtration systems designed to reduce specific health-related contaminants, such as Cryptosporidium, lead, volatile organic chemicals (VOCs) and asbestos that may be present in public or private drinking water.
The scope of this standard also includes material safety, structural integrity and other health-related contaminant reduction performance claims. The most common reduction claims verified by this standard are heavy metals, inorganics and volatile organic chemicals.

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