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Your Trusted Source For 20x20x4 Filters

We offer a complete selection of high-performance 20x20x4 HVAC filters. Whether you're replacing filters in your home, office, or commercial HVAC system, you'll find trusted options in MERV 1–13, including pleated, fiberglass, washable, and specialty filters.

All 20x20x4 filters are made in the USA and sourced from leading manufacturers like AAF Flanders and Koch Filter. Choose from standard and custom sizes to ensure a proper fit for your system—and enjoy clean air backed by over 50 years of HVAC experience.

Never Compromise on Quality When It Comes to the Air You Breathe

Forced air systems, including furnaces, air conditioners, and heat pumps, circulate warm or cool air throughout your home via ducts and vents. These systems utilize filters to prevent dust and debris from being distributed along with the conditioned air. These filters not only enhance indoor air quality but also safeguard your forced air system.

When filters become overly clogged with particles, they diminish your system's efficiency, leading to increased heating and cooling costs, due to the hindered air movement from your heating system into your home or business. A severely clogged filter can cause a build-up of hot air near your heating system, triggering its emergency shut-off mechanism and leading to intermittent operation. Furthermore, clogged filters can exacerbate the presence of mold, dust, and other allergens in your home.

What MERV Rating Is Right for You?

MERV (Minimum Efficiency Reporting Value) measures how well an air filter captures particles. A higher number means better filtration—but it must still be compatible with your HVAC system. Here's a breakdown to help you choose the right filter for your home or business.

MERV 1–4

Basic protection. Captures larger particles like dust, lint, and pollen. Minimal airflow resistance. Best for older systems or basic residential use.

✔ Highest airflow
✘ Does not trap fine particles

MERV 8

Great balance of airflow and filtration. Captures mold spores, dust mites, pet dander, and pollen. Most common choice for residential HVAC systems.

✔ Good airflow
✔ Effective for everyday air quality needs

MERV 10

Enhanced dust-holding capacity and improved particle removal compared to MERV 8. Traps finer particles like mold spores, hair spray, and fabric fibers.

✔ More efficient than MERV 8
✔ Still maintains strong airflow

MERV 11

Captures smaller particles like auto emissions, smoke, and some airborne bacteria. Ideal for homes with pets or allergy concerns. Moderate impact on airflow.

✔ Great for allergies
✘ May reduce airflow in older systems

MERV 13

Highest residential-grade filtration. Captures airborne bacteria, tobacco smoke, and fine particles. Recommended for asthma, smoke exposure, or medical-grade needs.

✔ Best indoor air quality
✘ Not suitable for all systems without airflow evaluation
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How to Measure HVAC Filters

To find the correct replacement, measure the length, width, and depth of your existing filter. Most filters are labeled with a nominal size (like 16x24x1), which is a rounded number—actual measurements are often slightly smaller. Accurate sizing ensures a proper fit and helps maintain airflow efficiency.

How to Measure HVAC Filter

Step 1: Remove Old Filter

Turn off your system and remove the existing filter. Look for printed dimensions on the frame—this is usually the nominal size.

Step 2: Measure Actual Size

Use a tape measure to get exact dimensions (length × width × depth). Round down to the nearest 1/8" if needed—example: 15-5/8" × 23-5/8" × 3/4".

Step 3: Match or Order Custom

If your measurements don’t match a standard size, we offer custom filters made to your exact dimensions.

Do you have an odd size filter?

Crafted with exact dimensions for a perfect fit, our filters effectively trap dust, pollen, and other indoor air pollutants, ensuring cleaner, healthier air in your surroundings.

Shop Custom Filters

Breathe Easier with Top-Quality Air Filters

Discover the ease of maintaining clean, healthy indoor air with RememberTheFilter.com. As a trusted provider of top-quality air filters since 2006, we offer a diverse range of products to meet all your residential and commercial needs. From custom furnace and AC filters to popular picks for forced air systems, we have it all. Plus, enjoy the benefits of free shipping, easy returns, and a user-friendly member portal for effortless subscription management. Choose RememberTheFilter.com for superior air filtration solutions and breathe easier in your home or business.

RememberTheFilter.com for Premium HVAC Filters & Expert Service

With nearly 20 years online and over 50 years of combined HVAC filter experience, we’re more than just a retailer—we’re filtration experts. As a proud member of the National Air Filtration Association (NAFA), we serve residential, commercial, and government customers across the U.S. Our filters are made in America and sourced from leading manufacturers like AAF Flanders, Koch Filter, and more.

We believe in clean air, fair prices, and helping people—not algorithms.

  • ✅ Nearly 20 years online helping homeowners and businesses nationwide
  • ✅ 50+ years of combined HVAC filtration experience
  • ✅ Member of NAFA – National Air Filtration Association
  • ✅ Made in the USA – filters from AAF Flanders, Koch, and more
  • ✅ Exact Filters® – custom built to your specs, down to 1/8"
  • ✅ Trusted by schools, clinics, and commercial buildings across the U.S.
  • Filter Fit Guarantee™
    Have concerns about ordering 20x20x4 filters online? Your purchase is backed by our Filter Fit Guarantee™.
  • Free Delivery
    We will ship your 20x20x4 filters direct to your door, for free! All orders in the domestic U.S over $50.
  • Real Human Service
    In America and we answer the phone. Call us at 1-866-469-8556.
  • Price Match
    Find a better price on the same filter? Let us know, we will beat it!