Replacement 18x24x4 air filters for homes, offices, and commercial HVAC systems. This collection covers every MERV rating we stock: fiberglass MERV 1–4, pleated MERV 8, MERV 10, MERV 11, and hospital-grade MERV 13.

20+ years in filtration 4.8 from 1,000+ reviews

39 products

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  • Koch MicroMAX FM Single Header 18x24x4 MERV 13 galvanized metal frame 4-inch minipleat filter
    MERV 13
    Koch

    18x24x4 MicroMAX FM Single Header MERV 13

    $843.75
    $843.75
    Case of 3 $281.25/filter
  • Koch MicroMAX FM Single Header 18x24x4 MERV 14 galvanized metal frame 4-inch minipleat filter
    MERV 14
    Koch

    18x24x4 MicroMAX FM Single Header MERV 14

    $837.06
    $837.06
    Case of 3 $279.02/filter
  • Koch MicroMAX 18x24x4 MERV 11 galvanized-metal-frame 4-inch extended-surface minipleat filter
    MERV 11
    Koch

    18x24x4 MicroMAX Galvanized Metal Frame MERV 11

    $509.79
    $509.79
    Case of 3 $169.93/filter
  • Koch MicroMAX 18x24x4 MERV 11 beverage-board-frame 4-inch extended-surface minipleat filter
    MERV 11
    Koch

    18x24x4 MicroMAX Beverage Board Frame MERV 11

    $338.79
    $338.79
    Case of 3 $112.93/filter
  • Koch MicroMAX 18x24x4 MERV 13 galvanized-metal-frame 4-inch extended-surface minipleat filter
    MERV 13
    Koch

    18x24x4 MicroMAX Galvanized Metal Frame MERV 13

    $624.45
    $624.45
    Case of 3 $208.15/filter
  • Koch MicroMAX 18x24x4 MERV 13 beverage-board-frame 4-inch extended-surface minipleat filter
    MERV 13
    Koch

    18x24x4 MicroMAX Beverage Board Frame MERV 13

    $392.16
    $392.16
    Case of 3 $130.72/filter
  • Koch MicroMAX 18x24x4 MERV 14 galvanized-metal-frame 4-inch extended-surface minipleat filter
    MERV 14
    Koch

    18x24x4 MicroMAX Galvanized Metal Frame MERV 14

    $626.58
    $626.58
    Case of 3 $208.86/filter
  • Koch MicroMAX 18x24x4 MERV 14 beverage-board-frame 4-inch extended-surface minipleat filter
    MERV 14
    Koch

    18x24x4 MicroMAX Beverage Board Frame MERV 14

    $396.03
    $396.03
    Case of 3 $132.01/filter
  • 18x24x4 AAF Flanders VariCel 2+ High Capacity Single Header MERV 15 3184627-904 (4 Filters)
    MERV 15
    AAF Flanders

    18x24x4 VariCel 2+ High Capacity Single Header MERV 15 3184627-904

    $547.97
    $547.97
    Case of 4 $136.99/filter
  • 18x24x4 AAF Flanders VariCel 2+ High Capacity No Header MERV 11 3184626-604 (4 Filters)
    MERV 11
    AAF Flanders

    18x24x4 VariCel 2+ High Capacity No Header MERV 11 3184626-604

    $524.22
    $524.22
    Case of 4 $131.06/filter
  • 18x24x4 Koch Multi-Pleat Boss Heavy Duty MERV 13 High Capacity 102-714-127 (6 Filters)
    MERV 13
    Koch

    18x24x4 Multi-Pleat Boss Heavy Duty MERV 13 High Capacity

    $532.32
    $532.32
    Case of 6 $88.72/filter
  • 18x24x4 Koch Multi-Pleat Boss Heavy Duty MERV 11 High Capacity 102-500-127 (6 Filters)
    MERV 11
    Koch

    18x24x4 Multi-Pleat Boss Heavy Duty MERV 11 High Capacity

    $295.99
    $295.99
    Case of 6 $49.33/filter
  • 18x24x4 Koch Multi-Pleat Boss Heavy Duty MERV 9 High Capacity 102-701-127 (6 Filters)
    MERV 9
    Koch

    18x24x4 Multi-Pleat Boss Heavy Duty MERV 9 High Capacity

    $282.99
    $282.99
    Case of 6 $47.17/filter
  • 18x24x4 Koch Multi-Pleat Green13 MERV 13 High Capacity 102-714-027 (6 Filters)
    MERV 13 HC
    Koch

    18x24x4 Multi-Pleat Green13 MERV 13 High Capacity

    $424.56
    $424.56
    Case of 6 $70.76/filter
  • 18x24x4 Koch Multi-Pleat XL11 MERV 11 High Capacity 102-500-027 (6 Filters)
    MERV 11 HC
    Koch

    18x24x4 Multi-Pleat XL11 MERV 11 High Capacity

    $268.99
    $268.99
    Case of 6 $44.83/filter
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Commercial & facilities

Need 18x24x4 by the pallet?

Volume pricing on any size or MERV, plus recurring delivery schedules. We handle facilities and commercial orders daily and can usually match or beat distributor pricing.

Request a quote 1-866-469-8556 Talk to a filter expert

18x24x4 HVAC, Furnace & AC Filters

Replacement 18x24x4 air filters for homes, offices, and commercial HVAC systems. This collection covers every MERV rating we stock: fiberglass MERV 1–4, pleated MERV 8, MERV 10, MERV 11, and hospital-grade MERV 13. Free shipping on orders over $50.

If your rack is labeled 18x24x4, any filter here will fit. Actual dimensions vary slightly by manufacturer—check the product page for exact specs. Need a non-standard size? Our custom filters cut to 1/8″ precision.

Which MERV Rating Should I Choose?

  • MERV 1–4 (fiberglass) — Lowest cost. Protects your blower and coil from debris but won't improve air quality. Best for rentals and monthly-change schedules.
  • MERV 8 (pleated) — Residential and light-commercial standard. Captures dust, pollen, lint, and mold spores.
  • MERV 10–11 — Captures pet dander, finer particulate, and some bacteria. Recommended for pets, allergies, and facilities pursuing better IAQ.
  • MERV 13 — Hospital-grade. Captures smoke, bacteria, virus carriers, and most airborne allergens. ASHRAE and CDC recommend MERV 13 where the HVAC system can support it.

Not sure? Take our MERV quiz or call 1-866-469-8556.

How Often Should I Change a 18x24x4 Filter?

4″ media cabinets hold dramatically more filter media than 1″ or 2″ filters, so they run longer between changes—typically every 6–12 months. Fewer changes per year, less labor, and typically lower total cost of ownership. A 6-month or annual subscription matches the natural changeout cycle.

Why Buy From RememberTheFilter.com

  • Trusted brands — AAF Flanders, Koch, and our own PrimeShield line, built by manufacturers we've partnered with for nearly two decades.
  • Filter Fit Guarantee — if it doesn't fit as expected, we'll make it right.
  • Free shipping over $50 to the lower 48, subscription discounts up to 10%, commercial & bulk pricing available.