Filter King FKFD21X21-12 21x21x1 MERV 13 Air Filters, 12-Pack

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Product guide

Filter King FKFD21X21-12 21x21x1 MERV 13 Air Filters, 12-Pack

Filter King FKFD21X21-12 is a 12-pack of MERV 13 replacement filters listed for 21x21x1 AC and furnace applications. The listing gives the actual size as 20.5 x 20.5 x .75 inches, so confirm those measurements against your filter slot before ordering.

At a glance

MERV 13 pleated filter, according to the listing.
Listed for residential air conditioners and furnaces, with slide-in installation.
The manufacturer recommends replacing 1-inch filters every 30 to 90 days and says these can last up to 90 days.

Price

$126.58Save 18%

Reference price: ~~$154.68~~

Price checked: Nov 14, 2026

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Pros and cons

Pros

A 12-pack provides multiple replacements for recurring filter changes.
The listing provides both nominal and actual dimensions, useful for checking fit before purchase.
The stated MERV 13 rating and AC/furnace compatibility make the intended application clear.

Technical specifications

12 specifications

Identity
Brand	Filter King
Model	FKFD21X21-12

Filtration and compatibility
MERV rating	13
Compatible devices	Air Conditioner, Furnace
Compatible HVAC systems	residential
Shape	Rectangular
Mounting type	Slide In

Dimensions and installation
Listed dimensions	21"L x 21"W x 0.75"Th
Advertised nominal size	21" x 21" x 1"
Actual size	20.5" x 20.5" x .75"

Materials and pack size
Material	Polypropylene
Quantity	12

What to know before buying

Listing details to confirm

The listing gives a nominal size of 21 x 21 x 1 inches and an actual size of 20.5 x 20.5 x .75 inches. Customer feedback also includes mixed size and fit reports, including concerns that the size differs from 15.75 x 15.75 inches and that fit can be loose. Verify your slot dimensions and the selected listing details before ordering.

What’s in the box

Included

Air filter (12)

Who is it for?

A good fit for

Households whose filter slot accepts the listed actual dimensions and uses a compatible residential AC or furnace.
Buyers looking for a multi-filter supply with a stated MERV 13 rating.

Less suited to

Buyers who have not checked their filter slot dimensions or need a filter with a different actual size.

Filter King FKFD21X21-12 21x21x1 MERV 13 Air Filters, 12-Pack · photo 2 — Additional product photo 2

Customer reviews on Amazon

4.5 / 5 · 178 ratings

5 stars80%80%
4 stars7%7%
3 stars5%5%
2 stars2%2%
1 star6%6%

Customer feedback describes the filters as effective and good value, while reports about size and fit are mixed, including concerns about loose fit and a size differing from 15.75 x 15.75 inches. For buyers, that fit uncertainty matters because this product is listed at 20.5 x 20.5 x .75 inches actual size. The rating distribution is mostly five-star but includes lower ratings, so the aggregate does not resolve fit for a particular system.

Positive themes

Customers report that the filters work well.
Customers describe them as good value.

Negative themes

Some customers report a loose fit or a size that differs from 15.75 x 15.75 inches.

Mixed feedback

Customers disagree about whether the size fits as expected.

Frequently asked questions

What is the actual size of this filter?

The listing states 20.5 x 20.5 x .75 inches actual size, compared with a nominal 21 x 21 x 1 inches. Check these measurements against your filter slot.

How many filters are included?

The product is listed as a 12-pack.

How often should the filter be changed?

The manufacturer recommends changing 1-inch filters every 30 to 90 days and claims this filter can last up to 90 days. Actual replacement timing depends on your usage and conditions.

What do customers report about fit?

Feedback is mixed. Some customers say the size is right, while others report size differences and a loose fit. Compare the stated actual dimensions with your existing filter and slot.