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.