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TopTech TechPure TT-FM-2020 QB OEM 20x20x4 Replacement Furnace Filter - QwikBox(R)

Size Guide

TopTech TT-FM-2020 20x20x4 furnace filters are designed for the TechPure TT-MAC-2122 & TT-MAC-2020 air cleaners. They are rated at MERV 11 and remove many allergens, dust, pollen and other airborne pollutants. The new QwikBox(R) collapsed design provides for less chance of shipping damage and takes up less space so it is more convenient to keep spare filters on hand. Assembly required.

  • New QwikBox(R) Collapsed Design That Is Easy To Assemble Prior to Installation
  • MERV 11
  • TopTech TechPure OEM Original Equipment Replacement Air Filter
  • Fits TechPure TT-MAC-2122 & TT-MAC-2020 Air Cleaners
  • Actual Size 19.375" x 19.375" x 3.75"

Customer Reviews

Based on 14 reviews
Top Tech Filter

I love the quality and sturdiness of this HVAC filter. The prompt and speedy delivery of my filter was outstanding, as has been the case with previous ones I have ordered. The cardboard box it came packed in was sturdy and, as always, protected my filter from damage or malformation in transit.


I am very happy


Love getting a pre assembled filter and the fast service.

Ready and Waiting....

I have a filter waiting for our next maintenance and one to spare. I loved finding genuine pre-assembled TopTech 4" filters for our new Carrier HVAC system at such a great price. The company scheduled to do our biannual maintenance work would have charged twice as much per filter so we're sticking with Atomic who was also fast with their delivery. All around a great find for such an expensive necessity.

Buy With Confidence

Free shipping was very timely, packaging protected the filter, received pre-assembled filter in good shape, filter is from the original manufacturer with perfect form and fit. Totally satisfied and pleased with plans to order my next one Atomic Filters (as long as the price remains the same or lower).

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