20x25x4 Air Filters

A 20x25x4 air filter is a 4-inch-deep pleated filter for whole-home furnace, heat pump, and AC systems. 

Filterbuy cuts it to an actual 19.5" x 24.5" x 3.625" and builds it to last 6 to 12 months, in MERV 8, 11, and 13, from $14.83 per filter in bulk. 

One thing to check before you order: some brands print 20x25x4 on filters that are actually 4.38 inches deep. 

Make sure to measure the depth of your old filter first. It only takes a minute and saves you a return.

Key Takeaways

• Filterbuy 20x25x4 filters last 6 to 12 months, roughly three times as long as a 1-inch filter because the 4-inch depth holds about four times the media surface area.

• The right MERV rating depends on your household. MERV 8 handles most homes. Go higher for allergies, pets, smoke, or odors. The chart below breaks it down.

• Check both sizes before ordering. Your old frame says 20x25x4. A tape measure says 19.5" x 24.5" x 3.625". The frame number is for ordering; the tape measure number is what actually fits.

What Is A 20x25x4 Air Filter?

A 20x25x4 air filter is a pleated HVAC filter with a nominal size of 20 x 25 x 4 inches and an actual size of 19.5" x 24.5" x 3.625". It sits in a media cabinet rather than a 1-inch return grille, and it's one of the most common whole-home sizes in North America. In fact, furnaces, heat pumps, and central AC systems all use it.

The depth is the whole story with this size. Folding the media into a 4-inch frame packs in about four times the surface area of a 1-inch filter. More surface area means more room to catch dust and dander before the filter loads up, and lower resistance while it does. That's why a Filterbuy 20x25x4 lasts 6 to 12 months instead of the 1 to 3 you'd get from a 1-inch filter.

Which MERV Rating Should You Choose?

There's no single right answer, because the right rating depends on who lives in your house and what's in your air. A retired couple with no pets and a family with two dogs and a child with asthma should not buy the same filter.

Here's how to think through it:

• MERV 8 is our gold standard for most households. Everyday dust, pollen, and lint. If nobody in the house has allergies and you don't have pets, this is your filter — and it's the most affordable of the three.

• MERV 11 if you have allergies or pets. It steps up capture in the fine-particle range where pet dander and mold spores live.

• MERV 13 if smoke is a concern. Wildfire season, a wood stove, or a smoker in the house — MERV 13 captures the fine particles that make up most smoke.

MERV 8 Vs. 11 Vs. 13 At A Glance

Filterbuy pricing checked in August 2026, reviewed quarterly.

Not sure where to start? Start with MERV 8 and move up if your allergies or your nose tell you to. Our MERV ratings explained guide covers the full 1-to-16 scale if you want a deeper dive.

A quick note on the MERV scale: MERV stands for Minimum Efficiency Reporting Value, defined by ANSI/ASHRAE Standard 52.2. A filter's MERV rating is its worst score across three particle-size ranges, not its best. The number on the frame is a floor, not a ceiling.

Will A 20x25x4 Air Filter Fit Your System?

Pull out your current filter and read the frame. If it says 20x25x4, you're in the right place. No filter to check? Measure the slot and round each dimension up to the nearest inch. A slot around 19.5" x 24.5" x 3.625" takes a 20x25x4.

Two numbers matter here. The nominal size (20x25x4) is the rounded number printed on the frame; it's what you order by. The actual size (19.5" x 24.5" x 3.625") is what the filter really measures, and it's what determines fit. 

We cut every filter about half an inch under nominal on purpose: any tighter and it binds going in, any looser and air slips around the media instead of through it. Our air filter sizes chart shows the same convention across every size we make.

Which HVAC Systems Use A 20x25x4 Filter?

One Filter Label, Two Different Depths: Read This Before You Order

Not every filter labeled 20x25x4 is the same depth, and this is the detail that causes the most returns.

Our 20x25x4 measures 3.625 inches deep. Honeywell, Lennox, and Carrier sell filters under the same 20x25x4 label that measure about 4.38 inches deep. That's a three-quarter-inch difference on filters that share a name. Put the wrong one in, and you either can't close the cabinet or you leave a gap that lets unfiltered air sneak past the media.

This isn't a hypothetical mix-up; many shoppers ask about it constantly on retail listings, and Honeywell's own support team has had to confirm that their "20x25x4" actually measures 4-3/8 inches deep.

The fix takes one minute:

1. Pull your old filter and measure its depth: just the thickness, cardboard edge to cardboard edge.

2. 3.75 inches or less? You want a standard 20x25x4.

3. Between 4.25 and 4.5 inches? You want our 20x25x5, whatever your old label said.

4. No old filter? Measure the slot opening and subtract about half an inch.
   

Filterbuy makes both depths, so we have no reason to steer you toward the wrong one. And if your slot matches neither, we build custom air filters to any dimension. Call (855) 345-8289.

How Deep Is A 20x25x4 By Brand?

Filterbuy depth is a production-line spec. Other depths are as published by each manufacturer, checked in August 2026. Filtrete actual size confirmed against 3M's published listing dimensions (19.88 x 24.63 x 4.31).

"I don't want anyone to feel like they need an HVAC license just to pick the right filter. My job is to give you the straight answer, explain why it matters, and let you get back to your day."

— Customer Service Manager, Filterbuy

Where Should You Buy 20x25x4 Air Filters?

The short answer: order factory-direct at Filterbuy.com. Here's the honest case for it.

When you buy direct, you're buying from the people who made the filter. Every 20x25x4 order ships within 24 hours, free, from our U.S. factories in Alabama, Pennsylvania, and Utah, and reaches most of the country in one to three days. 

You get the full MERV range in this size, exact-cut sizing straight off our production line, and bulk pricing that roughly halves the per-filter cost. A six-pack brings the price of MERV 11 from $40.99 to $20.99 each, and auto-delivery takes another 5% off while making sure you never forget a change.

You'll also find Filterbuy filters at Home Depot and on Amazon, and if that's more convenient, they're the same filters. Just know what changes: retail shelves usually stock one MERV level, marketplace listings come from many sellers at many depths, and neither offers our bulk tiers. On Amazon, our MERV 11 single runs $39.66 (checked August 2026), so direct pricing wins even before the multi-pack math.

Buying Direct Vs. Retail Vs. Marketplace

Filterbuy, Home Depot, and Amazon figures checked in August 2026. Retail and marketplace pricing changes often; re-verify quarterly.

Need A 20x25x4 Air Filter Fast?

Most people don't think about their filter until it's overdue. Good news on two fronts.

First, you have more time than you think. A loaded 4-inch filter doesn't fail overnight, and a day or two won't hurt your system. Second, we're faster than you'd expect. Every 20x25x4 order ships free within 24 hours from factories and distribution centers across the country — most orders arrive in one to three days, no store run required. Worth knowing: 4-inch sizes sell out at hardware stores far more often than 1-inch sizes do.

And if the reason you're here is that you forgot? Auto-delivery sends the next filter before it's due, at 5% off. Set it once, and this stops being a thing you think about.

How Long Does A 20x25x4 Air Filter Last?

Filterbuy 4-inch filters are built to last 6 to 12 months. That's the real advantage of this size: where a 1-inch filter needs changing every one to three months, the 20x25x4's deeper pleats hold months more dust before airflow suffers — so you're changing it once or twice a year instead of four to twelve times.

Where you land inside that 6-to-12-month window depends on your home. Pets, allergies, wildfire smoke, and heavy HVAC use all push you toward the earlier end. A low-traffic home with clean outdoor air can ride the full year.

The habit that removes all guesswork: write the install date on the frame in marker, and give the filter a quick look every couple of months. If it looks loaded, it is. Change it.

Why Filtration Is Worth Getting Right

Your filter matters more than most people give it credit for, and the numbers behind that come from federal research, not filter marketing.

The EPA reports that Americans spend about 90% of their time indoors, where some pollutants run two to five times higher than outdoor levels, and it lists dust mites, mold, pet dander, and particulate matter among established asthma triggers. That makes your HVAC filter air-quality equipment, not just machine protection.

The audience for that air quality is large. Per the CDC's National Health Interview Survey, a quarter of U.S. adults and a fifth of children have a diagnosed seasonal allergy, exactly the case where stepping up to MERV 11 is worth the price. And a clean filter pays you back regardless: the Department of Energy finds that replacing a clogged filter cuts an air conditioner's energy use by 5 to 15%, calling it the quickest way to save on home cooling.

How To Properly Install A 20x25x4 Air Filter

1. Turn the system off.

2. Take a photo of the airflow arrow on the old filter before you pull it.

3. Slide the new filter in with the arrow pointing toward the furnace or blower.

4. Write the install date on the frame with a marker.

5. Turn the system back on.

Two minutes, done. The photo step is there because backward installation is the most common mistake our support team sees, and a photo settles the question instantly.

Frequently Asked Questions

Is A 20x25x4 Air Filter Really 4 Inches Thick?

No, and this catches a lot of people. The Filterbuy 20x25x4 measures 3.625 inches deep. Filters sold under the same label by Honeywell, Lennox, and Carrier measure about 4.38 inches. The number on the frame is a shopping label, not a measurement. Measure your old filter's depth before ordering: 3.75 inches or less means a 20x25x4, and 4.25 to 4.5 inches means a 20x25x5.

How Often Should You Change A 4-inch Air Filter?

Filterbuy 4-inch filters last 6 to 12 months. Homes with pets, allergy sufferers, or seasonal smoke should plan on the earlier end of that range. Low-traffic homes with clean air can go the full year. Check it every couple of months and change it when it looks loaded.

Can I Use A 20x25x5 Filter Instead Of A 20x25x4?

Only if your cabinet was built for it. The two differ by roughly three-quarters of an inch of depth, more than the quarter-inch of play most slots allow. A filter that's too deep won't seat, and one that's too shallow leaves a gap that unfiltered air flows straight through. Measure the slot depth and buy the size it was built for.

What MERV Rating Do I Need For A 20x25x4 Filter?

It depends on your household. MERV 8 covers most homes. Choose MERV 11 if you have pets or allergies, MERV 13 if smoke is a factor, and the Odor Eliminator if smells are the main complaint. The chart near the top of this page breaks it down.

Will A MERV 13 Filter Restrict My Airflow?

In a 4-inch cabinet, almost never. That concern comes from the 1-inch era, where dense media in a thin frame really did choke airflow. Spread the same rating across four times the surface area, and the resistance drops dramatically. If your system has a 4-inch slot, it was designed with filters like this in mind. Check the slot depth first and the MERV number second.

Do 20x25x4 Filters Help With Wildfire Smoke?

A MERV 13 in this size captures at least half of the particles in the 0.3 to 1.0 micron range, where most wildfire smoke sits, so it measurably cuts indoor smoke while the fan runs. During smoke events, keep windows closed, run the fan on continuous rather than auto, and check the filter more often. Smoke loads a filter much faster than everyday dust.

What Happens If I Install It Backwards?

Airflow resistance rises and efficiency drops. Pleated filters are directional: the wire backing supports the pleats in one direction only, so a reversed filter can collapse under load. The arrow on the frame points toward the furnace or air handler.

What Does A 20x25x4 Filter Cost Per Year?

Because these last 6 to 12 months, you're buying one or two filters a year. At six-pack pricing, that's $16.66 to $33.32 a year for MERV 8, $20.99 to $41.98 for MERV 11, and $23.33 to $46.66 for MERV 13. Compare that to changing a 1-inch filter every month or two, and the 4-inch usually comes out ahead on both cost and effort.

About The Author And Reviewer

Michelle Wan is Filterbuy's Brand Manager and Air Quality Writer, covering MERV ratings, filtration, and pressure drop across the company's resource library. She works directly with the manufacturing team across Filterbuy's U.S. production facilities, so her guidance comes from how filters are actually built and tested.

David Clark is a Licensed HVAC Technician and CEO of Filterbuy HVAC Solutions, whose crews take residential service calls year-round. He reviewed this page for technical accuracy.

Last reviewed and updated August 2026. We review this page quarterly and update pricing and specifications when they change.