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52

21x21x1 air filter

Worth a look

Shows sweet-spot pricing room ($26.30–$80.70), but brand-locked demand (top 5 brands take 100% of clicks) keeps it on the watch list.

Market size 53Growth 71Conversion 82Competition 20Returns 83Price range 95Avg price 92Brand share 0Review moat 43Quality gap 20

Price range

Incredible$26.30–$80.70

cheapest to priciest tracked listing — scored on the share inside $15–$100

Avg price

Great$54.08

avg listing price — sweet spot $15–$100

Returns

Great1.6%

return rate — above 5% kills the launch gate

Conversion

Great8.8%

search→purchase rate — share of searches ending in a sale

Growth

Good+53.4%

90-day search growth — must beat 0% to launch

Market size

Good$348K

$348K/yr · 73K searches

Review moat

Okay2,243.73

avg incumbent reviews — the moat a new listing must climb

Competition

Bad77%

top-5 click share — a locked-up shelf

Quality gap

Bad4.7★

avg incumbent rating — lower means beatable quality

Brand share

Bad100%

top-5 brand share — brand-locked demand

Signals High Price

According to Flapen's Amazon United States niche tracking, 21x21x1 air filter is a $348K/yr Amazon United States market (73K searches/yr). The top 5 brands hold 100% of demand. Demand peaks in Jun–Jul. Verdict: Worth a look — 52/100.

Data updated Jul 27, 2026 · scored weekly · How we score niches

21x21x1 air filter market data

Units sold / yr
6K–8K
avg 500–750/product
Revenue / yr
$324K–$433K
units × avg price
Conversion rate
8.8%
Avg BSR
#278
Page quality
0%
Prime
64%
Sponsored
73%
Out of stock
0.0%
Avg brand age
60 months
Avg seller age
209 days

Competition & brand share

The top 5 products capture 77% of clicks — a locked-up shelf that new listings rarely crack.

Brands

3 falling

Sellers

6

Top-5 brand share

100%

Top 20: 100%

Top-5 click share

77%

Top 20: 100%

Open market

0%

  • Filtrete49%
  • Aerostar38%
  • Filter King13%
  • Open — no brand owns it (0%)

Demand & seasonality

Weekly Amazon search volume, last 104 weeks — +53.4% search growth over the last 90 days.
2K2KSpike '25Prime Day '25Spike '26SepDecMarJunAugNovMarMay

Peak months: Jun, Jul · busiest ÷ quietest = 1.8×

Open Trend

Top 21x21x1 air filter search terms

  • 21x21x1 air filter36K/yr
  • ac filter 21x21x112K/yr
  • air filter 21x21x112K/yr
  • 21 x 21 x 1 air filter6K/yr
  • 21x21x1 furnace filter4K/yr
  • furnace filters 21x21x14K/yr
All search terms

Top 21x21x1 air filter products on Amazon

Each bubble is one product — market share against review moat; bubble size tracks estimated sales, color grades how beatable the incumbent looks.

0%10%$35K20%$70K30%$104K40%$139K101001K10K100K Reviews — right = deep review moat Market share (90d) ≈ est. sales
Beatable (≤4.3★) Contested Strong incumbent (>4.7★)

All 11 tracked products in this niche — three views at once, no toggling.

Top sellers

by 90-day click share
1
Aerostar 21x21x1 MERV 8 Pleated Air Filter AC Furnace Air Filter 6 Pack (Actual Size: 20 7/8 x 20 7/8 x 3/4)

Aerostar 21x21x1 MERV 8 Pleated Air Filter AC Furnace Air Filter 6 Pack (Actual Size: 20 7/8 x 20 7/8 x 3/4)

Aerostar$49.644.8★615 rev

2
Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 4-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 4-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$43.654.7★6,265 rev

3
Aerostar 21x21x1 MERV 11 Air Filter 6 Count ACTUAL SIZE (20.88 x 20.88 x 0.75) HVAC Air Conditioning & Furnace Filter for Dust Pet Dander Smoke & Allergies (MPR 1200 / FPR 7) Made in USA

Aerostar 21x21x1 MERV 11 Air Filter 6 Count ACTUAL SIZE (20.88 x 20.88 x 0.75) HVAC Air Conditioning & Furnace Filter for Dust Pet Dander Smoke & Allergies (MPR 1200 / FPR 7) Made in USA

Aerostar$57.444.8★615 rev

4
Filtrete 21x21x1 Air Filter MERV 11 MPR 1000 Allergens & Pet Dander 3-Month AC and Furnace Filters Cleaner Air Reliable Airflow 6 HVAC Filters (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 Air Filter MERV 11 MPR 1000 Allergens & Pet Dander 3-Month AC and Furnace Filters Cleaner Air Reliable Airflow 6 HVAC Filters (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$72.994.8★11,774 rev

5
Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 6-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 6-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$48.014.6★627 rev

Newest

by launch date
Filter King 21x21x1 Air Filter | 12-PACK | MERV 11 HVAC Pleated A/C Furnace Filters | MADE IN USA | Actual Size: 21 x 21 x .75

Filter King 21x21x1 Air Filter | 12-PACK | MERV 11 HVAC Pleated A/C Furnace Filters | MADE IN USA | Actual Size: 21 x 21 x .75

Filter King$80.7014 rev

7mo ago
Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 2-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 2-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$26.30740 rev

1y ago
Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 4-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 4-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$43.656,265 rev

1y ago
Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 6-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 6-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$48.01627 rev

1y ago
Filter King 21x21x1 Air Filter (MERV 13) (6-Pack) Dust & Allergy Control AC Furnace Filters MADE IN USA HVAC Pleated Electrostatic (Actual Size: 20.5 x 20.5 x .75)

Filter King 21x21x1 Air Filter (MERV 13) (6-Pack) Dust & Allergy Control AC Furnace Filters MADE IN USA HVAC Pleated Electrostatic (Actual Size: 20.5 x 20.5 x .75)

Filter King$61.6226 rev

2y ago

Trending

90-day click momentum
Filter King 21x21x1 Air Filter (MERV 8) (6-Pack) Dust & Allergy Control AC Furnace Filters MADE IN USA HVAC Pleated Electrostatic (Actual Size: 20.5 x 20.5 x .75)

Filter King 21x21x1 Air Filter (MERV 8) (6-Pack) Dust & Allergy Control AC Furnace Filters MADE IN USA HVAC Pleated Electrostatic (Actual Size: 20.5 x 20.5 x .75)

Filter King$54.864.5★

▲ 125%
Aerostar 21x21x1 MERV 8 Pleated Air Filter AC Furnace Air Filter 6 Pack (Actual Size: 20 7/8 x 20 7/8 x 3/4)

Aerostar 21x21x1 MERV 8 Pleated Air Filter AC Furnace Air Filter 6 Pack (Actual Size: 20 7/8 x 20 7/8 x 3/4)

Aerostar$49.644.8★

▲ 57%
Filtrete 21x21x1 Air Filter MERV 11 MPR 1000 Allergens & Pet Dander 3-Month AC and Furnace Filters Cleaner Air Reliable Airflow 6 HVAC Filters (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 Air Filter MERV 11 MPR 1000 Allergens & Pet Dander 3-Month AC and Furnace Filters Cleaner Air Reliable Airflow 6 HVAC Filters (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$72.994.8★

▲ 28%
Aerostar 21x21x1 MERV 13-4 Count - Pleated HVAC Furnace & Air Conditioner Filters - Removes Bacteria Dust Cold & Flu Germs Lint Mold Pet Dander Allergy-Causing Pollen Smog Smoke & Viruses

Aerostar 21x21x1 MERV 13-4 Count - Pleated HVAC Furnace & Air Conditioner Filters - Removes Bacteria Dust Cold & Flu Germs Lint Mold Pet Dander Allergy-Causing Pollen Smog Smoke & Viruses

Aerostar$55.724.8★

▲ 25%
Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 6-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete 21x21x1 AC Furnace Air Filter MPR 700 MERV 8 Tough on Pollen Easy on Airflow 3-Month Pleated 1-Inch Electrostatic Air Cleaning Filter 6-Pack (Actual Size 20.81 x 20.81 x 0.81 in)

Filtrete$48.014.6★

▲ 14%

What buyers say about 21x21x1 air filter

What buyers praise and complain about, mined from review topics.

What buyers love

Quality-Overall38%

“great quality”

Filtration19%

“These filters do the job”

Size-Overall13%

“Perfect fit, great quality”

Value For Money6%

“Good for the money”

Allergies6%

“MERV 8 is recommended for most systems unless you have severe allergies”

Advertised Vs Actual Product6%

“As advertised”

Material Quality6%

“Materials are good-However”

What buyers complain about

Strength33%

“Not sturdy enough tends to sag”

Filtration33%

“These are poorly made filters”

Size-Overall13%

“Not true to size”

Noise Level8%

“so I either deal with the noise or just take my loss”

Top return reasons

Size-Overall88%
Filtration5%
Compatibility-Overall2%
Advertised Vs Actual Product2%
Thin1%
Quality-Overall1%
Functionality-Overall1%
Durability0%
Value For Money0%
Material Quality0%

Common questions

Is 21x21x1 air filter profitable to sell on Amazon United States?
The niche generates $348K/yr across 11 tracked products. 1 of 1 products launched in the last 360 days are still selling. 90-day search growth is +53.4%. Flapen's verdict: Worth a look (52/100).
How competitive is the 21x21x1 air filter niche?
3 brands and 6 sellers compete. The top 5 products take 77% of clicks and top 5 brands hold 100% of demand.
What do buyers complain about in 21x21x1 air filter?
Top complaints mined from reviews: Strength, Filtration, Size-Overall. The return rate is 1.6%.
When does demand for 21x21x1 air filter peak?
Demand peaks in Jun–Jul; the busiest month runs 1.8× the quietest.
What does it cost to enter the 21x21x1 air filter niche?
Listings span $26.30–$80.70; the average listing price is $54.08 (sweet spot $15–$100). The average incumbent carries 2,244 reviews — the moat a new listing must climb.