Fits checked Oct 1, 2026 · How we check
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AprilAire · media air cleaner · media air cleaner cabinet

AprilAire U121 replacement filter

Use part UK211, or any one of UK213. Lasts up to 12 months.

Any one of these fits · standard choice

Maker lists this model

AprilAire UK211 MERV 11 + rails

AprilAire UK211 (Replaces 210) MERV 11 TriPure Filter + Upgrade Rails

Part number
UK211
How many
1 per unitpacks: UK211 02 (2), UK211 04 (4)
How often
Lasts up to 12 months
Size
20 x 25 x 4 in20 x 25 x 4 in nominal (21.44 x 27 x 3.68 actual)

AprilAire lists the U121 on the UK211 page (MERV 11); the UK211 bundles one-time upgrade rails that older cabinets need, and the filter-only refill is the 3F211.

Buy UK211 MERV 11 + rails on AmazonManufacturer page

Opens an Amazon search for AprilAire UK211 MERV 11 + rails. Check the listing says UK211.

See the sources

Compare the 2 options

The U121 holds one filter at a time. Any one of these fits; AprilAire ships it with the first one.

FilterGradeSizeHow oftenBuy
UK211 MERV 11 + railsUK211standard choiceMERV 11 TriPure 3-inch filter, one-time upgrade rails20 x 25 x 4 inLasts up to 12 monthsAmazon
UK213 MERV 13 + railsUK213MERV 13 TriPure 3-inch filter, one-time upgrade rails20 x 25 x 4 inLasts up to 12 monthsAmazon

Other genuine options from AprilAire

Variants and kits the maker sells for this model. Same fit, different media or packaging.

  • 3F211 filter only (ships in the U121; AprilAire's subscription refill)
    3F211 · Find on Amazon

Sources

High confidence: the manufacturer names this exact model on a live page. Each line is the page we read and the day we read it.

  • Which filter fits shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Compatible Models: 1210, 1620, 2120, 2200, 2210, 2216, 3210, 4200, U121, U223, U226, U162, U172
  • How many shop.aprilaire.com Maker's own page checked Oct 1, 2026
    INCLUDED IN THE BOX: (1) U121 Air Purifier (1) 3F211 Air Filter; Filter Nominal Dimensions (H x W): 20 x 25 (inches)
  • How often shop.aprilaire.com Maker's own page checked Oct 1, 2026
    LONG FILTER LIFE – One filter lasts up to 12 months
  • Size shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Nominal Measurements: 20H x 25W x 4D (inches) Actual Measurements: 21.44H x 27W x 3.68D (inches)
  • What's in it shop.aprilaire.com Maker's own page checked Oct 1, 2026
    MERV Rating: 11; Materials: Plastic, Synthetic Fiber
  • Packs shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Package sizes: 1-pack UK211; 2-pack UK211 02; 4-pack UK211 04
Show all 17 sources

Which filter fits

  1. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Compatible Models: 1210, 1620, 2120, 2200, 2210, 2216, 3210, 4200, U121, U223, U226, U162, U172
  2. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Compatible Models: 1210, 1620, 2120, 2200, 2210, 2216, 3210, 4200, U121, U223, U226, U162, U172
  3. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Page for the U121 (per its URL): Replaces AprilAire 1210 Whole-House Air Purifier
  4. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Product 'AprilAire UK211 (Replaces 210) MERV 11 TriPure Filter + Upgrade Rails', SKUs UK211, UK211 02, UK211 04
  5. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    The AprilAire UK211 replaces the sunsetting AprilAire 210 Filter; 'Your next subscription will be the 3F211 - filter only'
  6. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    NEW AND IMPROVED U162 20 x 25 EASY INSTALL WHOLE-HOUSE AIR PURIFIER (LEFT RETURN DROP) with revolutionary new AprilAire 3F211 MERV 11 3" Air Filter
  7. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Product 'AprilAire UK213 (Replaces 213) MERV 13 TriPure Filter + Upgrade Rails', SKUs UK213, UK213 02, UK213 04
  8. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    The AprilAire UK213 replaces the sunsetting AprilAire 213 Filter; 'Your next subscription will be the 3F213 - filter only'

How many

  1. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    INCLUDED IN THE BOX: (1) U121 Air Purifier (1) 3F211 Air Filter; Filter Nominal Dimensions (H x W): 20 x 25 (inches)

How often

  1. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    LONG FILTER LIFE – One filter lasts up to 12 months
  2. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    LONG FILTER LIFE – One filter lasts up to 12 months

Size

  1. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Nominal Measurements: 20H x 25W x 4D (inches) Actual Measurements: 21.44H x 27W x 3.68D (inches)
  2. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Nominal Measurements: 20H x 25W x 4D (inches) Actual Measurements: 21.44H x 27W x 3.68D (inches)

What's in it

  1. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    MERV Rating: 11; Materials: Plastic, Synthetic Fiber
  2. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    MERV Rating: 13; Materials: Plastic, Synthetic Fiber

Packs

  1. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Package sizes: 1-pack UK211; 2-pack UK211 02; 4-pack UK211 04
  2. shop.aprilaire.com Maker's own page checked Oct 1, 2026
    Package sizes: 1-pack UK213; 2-pack UK213 02; 4-pack UK213 04