Does Furnace Filter Thickness Matter? (2020 Guide)

Do you want to know if furnace filter thickness matters to your HVAC performance?

Thicker furnace filters, known as media filters, almost always do a better job than cheaper one inch filters.

In this guide, I will go over...

  • Benefits of thicker media furnace filters
  • Installation tips
  • How often to change thicker furnace filters

Let's get started with this guide!

does furnace filter thickness matter

Why Do Thicker Furnace Filters Work Better?

Pretty much any HVAC pro will tell you that thicker filters do a better job than the common 1-inch furnace filters. Thicker filters, known as media filters, are generally 4 to 5 inches thick as compared to the ubiquitous 1-inch filters that you can even buy in grocery stores.

The reason media filters do a better job is because they have more surface area. These 4-inch media filters can have 20-30 feet of surface area with its pleated (accordian) filter material. Since there is more surface area, it can catch more debris without clogging up as quickly.

This also means that it is less restrictive to air flow, which helps the HVAC system run more efficiently. So not only will it clean the air better, but you will get much more air flow than the standard one inchers.

Read Also: What Are The Best Furnace Filters For Mold?

Media Filters Seal Better

Thicker media filters tend to seal in the filter cabinet much better than one inch filters.

These media filters have much stiffer cardboard frames, and some media filters even have plastic 'rails' on the top and bottom so you can slide it into the furnace with a very tight seal. Poorly fitted one inch filters where air goes around the frame (even causing the frame to bend and warp) is very common.

Regardless of the filter you go with, try to make sure it fits snugly as much as possible.

Read Also: Can You Run A Furnace Without A Filter Temporarily?

Thicker Filters Save Money

High-capacity media furnance filters will also save homeowners money. With media filters, you only have to replace them every 6-months to a year. With 1-inch filters, you have to replace them at least every 3-months, but a lot of people replace them monthly.

And someone may get the bright idea to just buy multiple 1-inch filters, and stack them on top of each other. But this is extremely harmful to your HVAC system.

When you stack 1-inch filters together, you are creating multiple layers for the air to pass through. With media filters, it is still a single filter layer, it just has much more surface area.

If you put multiple 1-inch filters together, that is similar to putting 5 coffee filters together and trying to brew a cup of coffee — it just doesn't work.

Read Also: What Are The Best Furnace Filters For Dust Control?

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Thicker Filters Improve HVAC Performance

High efficiency media filters will improve HVAC performance and longevity.

Since there is more surface area, more air can pass through the system, which puts significantly less strain on the motor, compressor, coil, and other components. And you will have a more comfortable home environment, because there is more air flow, and it will heat your target temperature more easily.

For comparison, a 4-inch thick filter will have approximately twice the surface areas as a 2-inch thick filter. The higher surface area will potentially reduce the pressure drop at the same time that you increase the MERV efficiency rating.

One of the most common complaints I had during home inspections is the low air flow at vents. And the first thing I always checked was the furnace filter, because a clogged one inch filter get dirty so easily.

Read Also: What Is The Difference Between MERV And MPR Filter Ratings?

How To Install A Thicker Media Furnace Filter?

The best place to install media filters is at the furnace itself rather than the return vent.

If you install a media filter at the return vent, it will cause a pressure drop in the return duct. If the return duct isn't perfectly sealed — it will cause air leaks — and create a negative pressure balance in your system.

So if you absolutely have to install these thicker filters at a return grille, I would recommend having your return duct thoroughly sealed and air tight. However, with most HVAC systems, you should be able to retrofit a media filter cabinet either underneath the furnace or at the side.

Read Also: What Are The Best Furnace Filters For Odors?

MERV Rating

And even though media filters produce more air flow (less of a pressure drop), and clog less easily — you still want to be careful about the MERV rating.

The MERV rating is basically a measurement of how well the filter captures particles in the 0.3 to 10 micron size range. The higher the MERV rating, the better the furnace filter. But a higher MERV filter also tends to reduce the amount of air flow.

I recommend consulting with your HVAC system literature or with an HVAC tech for the proper MERV rating that your system can handle. After you install the high efficiency media filter, you can also have a HVAC pro measure the pressure drop in your system to make sure that is satisfactory.

Also, if you have a variable speed blower in your system, this can probably handle a higher MERV rating than single speed systems.

Read Also: What Happens If My Furnace Filter Is Backwards?

Final Thoughts

Personally, as a home inspector, I recommend installing a 4-5 inch media filter if it is possible for your system. Most HVAC systems can be retrofitted to fit these thicker high efficiency filters.

Your system will run better with more air flow, and the filter won't clog as easily. In addition, you only have to change media filters every 6-months to 12-months.

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Arie Van Tuijl

Arie Van Tuijl

Arie is the founder of Home Inspector Secrets, an online resource dedicated to helping people understand how homes work. He is a licensed home inspector in two U.S states and owns a residential and commercial inspection company (read his full bio on the About page). To ask Arie a question, please use the comment box at the bottom of the relevant article.

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Home Inspector Secrets is an online resource for owners, buyers, and sellers to understand all aspects of home maintenance. We have detailed home guides, product reviews, inspection advice, and much more.