---
title: "21x21x1 Air Filter — $348K/yr Amazon US Niche (2026) - Flapen"
canonical_url: "https://flapen.com/research/us/tools-home-improvement/21x21x1-air-filter"
last_updated: "2026-08-08T08:50:39.344Z"
locale: en
meta:
description: "Niche score 52/100 · $348K/yr market. Brand-locked demand (top 5 brands take 100% of clicks) keeps it on the watch list. Data updated Jul 2026."
"og:description": "Niche score 52/100 · $348K/yr market. Brand-locked demand (top 5 brands take 100% of clicks) keeps it on the watch list. Data updated Jul 2026."
"og:title": "21x21x1 Air Filter — $348K/yr Amazon US Niche (2026) - Flapen"
---
# **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**
**Great****1.6%**
return rate — above 5% kills the launch gate
**Conversion**
**Great****8.8%**
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**
**Okay****2,243.73**
avg incumbent reviews — the moat a new listing must climb
**Competition**
**Bad****77%**
top-5 click share — a locked-up shelf
**Quality gap**
**Bad****4.7★**
avg incumbent rating — lower means beatable quality
**Brand share**
**Bad****100%**
top-5 brand share — brand-locked demand
**Signals**[** High Price**](https://flapen.com/research/niches?market=us&signal=high_price "Avg price > $50")
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 ~~](https://flapen.com/research/methodology)
## **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 '26 seasonSepDecMarJunAugNovMarMay
Peak months: Jun, Jul · busiest ÷ quietest = 1.8×
[**Open Trend **](https://flapen.com/research/us/tools-home-improvement/21x21x1-air-filter/trend)
## **Top 21x21x1 air filter search terms**
- **21x21x1 air filter**36K/yr+42.5%6.2% conv. - **ac filter 21x21x1**12K/yr+57.6%5.0% conv. - **air filter 21x21x1**12K/yr+46.0%4.3% conv. - **21 x 21 x 1 air filter**6K/yr+100.8%6.7% conv. - **21x21x1 furnace filter**4K/yr+81.9%0.2% conv. - **furnace filters 21x21x1**4K/yr+87.0%0.6% conv. [**All search terms **](https://flapen.com/research/us/tools-home-improvement/21x21x1-air-filter/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 moatMarket 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**$49.64**4.8★615 rev](https://www.amazon.com/dp/B0CLPG6R11) [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**$43.65**4.7★6,265 rev](https://www.amazon.com/dp/B0DMTG4CWD) [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**$57.44**4.8★615 rev](https://www.amazon.com/dp/B0B1G56TTW) [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**$72.99**4.8★11,774 rev](https://www.amazon.com/dp/B07CZW8HMK) [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**$48.01**4.6★627 rev](https://www.amazon.com/dp/B0DMTGGR8W)
**~~View all top sellers →~~**
### **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**$80.70**14 rev7mo ago](https://www.amazon.com/dp/B0CZMBPBSZ) [**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**$26.30**740 rev1y ago](https://www.amazon.com/dp/B0F9LRZ75G) [**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**$43.65**6,265 rev1y ago](https://www.amazon.com/dp/B0DMTG4CWD) [**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**$48.01**627 rev1y ago](https://www.amazon.com/dp/B0DMTGGR8W) [**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**$61.62**26 rev2y ago](https://www.amazon.com/dp/B0CZLXGG48)
**~~View all new products →~~**
### **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**$54.86**4.5★**▲ 125%**](https://www.amazon.com/dp/B07HFGVBSK) [**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**$49.64**4.8★**▲ 57%**](https://www.amazon.com/dp/B0CLPG6R11) [**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**$72.99**4.8★**▲ 28%**](https://www.amazon.com/dp/B07CZW8HMK) [**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**$55.72**4.8★**▲ 25%**](https://www.amazon.com/dp/B09P47S9X3) [**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**$48.01**4.6★**▲ 14%**](https://www.amazon.com/dp/B0DMTGGR8W)
**~~View all trending →~~**
## **What buyers say about 21x21x1 air filter**
What buyers praise and complain about, mined from review topics.
### **What buyers love **
**Quality-Overall**38%
*“great quality”*
**Filtration**19%
*“These filters do the job”*
**Size-Overall**13%
*“Perfect fit, great quality”*
**Value For Money**6%
*“Good for the money”*
**Allergies**6%
*“MERV 8 is recommended for most systems unless you have severe allergies”*
**Advertised Vs Actual Product**6%
*“As advertised”*
**Material Quality**6%
*“Materials are good-However”*
### **What buyers complain about **
**Strength**33%
*“Not sturdy enough tends to sag”*
**Filtration**33%
*“These are poorly made filters”*
**Size-Overall**13%
*“Not true to size”*
**Noise Level**8%
*“so I either deal with the noise or just take my loss”*
### **Top return reasons **
**Size-Overall**88%
**Filtration**5%
**Compatibility-Overall**2%
**Advertised Vs Actual Product**2%
**Thin**1%
**Quality-Overall**1%
**Functionality-Overall**1%
**Durability**0%
**Value For Money**0%
**Material Quality**0%
## **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.
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