What Are The Most Common Air Filter Sizes?

An air filter is an essential component of your home. From filtering out harmful contaminants to keeping your HVAC unit running efficiently, these products have several benefits.

However, while filters provide many advantages for your system, your home, and your health, they must be changed on a regular basis. Additionally, it's also important to understand the filter size you need.

In this article, we'll talk more about these essential HVAC products, including which sizes are the most common and how to find the perfect fit.

Most Common Furnace and AC Filter Sizes

When it comes to AC and furnace filters, it's essential to understand the size you need. Air filters are labeled with three different dimensions. The first number relates to the product's length, the second number is the width, and the last number is the thickness or depth.

Here are some of the most common furnace and AC filter sizes:

• 10 X 20 X 1’’
• 14 X 20 X 1’’
• 16 X 24 X 1’’
• 18 X 30 X 1”
• 20 x 20 x 1
• 16 x 25 x 1
• 20 x 25 x 1
• 20 x 25 x 4
• 16 x 20 x 1
• 16 x 25 x 4
• 20 x 30 x 1
• 12 x 12 x 1
• 14 x 14 x 1

These are the sizes you'd probably see when visiting a home supply store. These numbers relate to the standard size of the return air vents in your home, responsible for controlling the air movement to and from your HVAC unit.

Is Your Filter the Wrong Size?

Unfortunately, many people install an improperly-sized filter, which can lead to some problems. For one, this can greatly affect the number of air contaminants that are filtered out, leading to poor indoor air quality. Secondly, this issue can also cause your HVAC system to work harder than it should, potentially causing numerous problems with your HVAC unit.



Worried you may have installed the incorrect air filter? Here are some signs that you're using the wrong size:

• You hear rattling noises—this may indicate the filter is too small
• The filter must be forced into place to fit—this means it's too large
• Your home is more dusty than usual—this could indicate the filter is too small
• You notice bent corners on the filter when removed—which means it could be too large
  

How to Check the Filter Size I Need

Not sure about the correct filter size for your home? While knowing the size seems pretty straightforward, it can be more difficult than you think. Furthermore, if you buy the wrong size, there can be some serious consequences. For one, you may notice higher energy bills, a poorly functioning system, and even health problems.

It's important to note that there doesn't have to be an airtight seal between the frame and air filter. However, it should fit fairly snug with a small amount of space around the edges. If you have to force the filter into place, you probably need a different size. The goal is to have the filter slide into the frame comfortably with a little wiggle room, but not too much.

If you're unsure about the filter size you need, you may have to do some measuring. However, before completing this step, it's important to understand the difference between nominal and actual filter sizes.

Finding the Perfect Fit

When it comes to AC and furnace filter sizes, manufacturers estimate these numbers. This is called the nominal size. No matter what brand you choose, the filter's nominal size will stay the same. Still, it's important to understand how this nominal size compares to the actual size.

Nominal Size

The nominal size is just an estimate from the manufacturer. This number is typically displayed on the side of the filter. The nominal size is a rounded estimate, used for consistency reasons. In the production process, every filter won't be the same exact size. If the manufacturer measured the actual size, the variation of numbers would confuse shoppers. This nominal size creates consistency across the board, adding peace of mind and less confusion for consumers. This also makes it easier to compare different filter models.

Actual Size

Simply put, the actual size of an air filter relates to its exact size. If you were to measure your home's air filter, you'll get these exact measurements. Typically, nominal AC and furnace filter sizes are 1/4" to 1/2" bigger than the actual size. Luckily, if you know your filter's actual size, figuring out the nominal size is easy. All you have to do is round each dimension up to the nearest inch.

DIY Measurements

Not sure about the actual size of your filter? If not, the easiest place to check is your existing filter, but only if it fits correctly. To check the size, power off your system, remove the filter from the compartment, and look at the dimensions. If your filter fits properly with no issues, then this is the size you need.

However, in order to know the exact size, you'll want to take the measurements yourself. To get started, go ahead and use a tape measure or flat ruler to measure each side of the filter. This includes the length, width, and thickness or depth. You should measure these in inches, which will give you your exact dimensions.

Another option to determine size involves measuring the frame that the filter fits into. However, this can be a difficult process. To get started, turn off your system and open the compartment. Then, measure the length, width, and depth of the slot. Keep in mind that AC and furnace filter sizes should be smaller than the measurements of the filter compartment.



As this process can be complicated and may lead to inaccurate readings, we recommend measuring the filter instead.

Is a Thicker Air Filter Better?

The majority of furnace and AC filter sizes include a 1-inch thickness. While this is standard in many homes, some are equipped with thicker filters. These have the ability to handle more buildup, meaning you'll need to change them less often. Furthermore, a thicker filter can trap more particles than a standard filter. However, these filters can sometimes restrict airflow, potentially leading to system and air quality issues.

Final Thoughts

Understanding more about AC and furnace filter sizes can ensure you find the perfect size for your home. By using a properly-sized filter and changing it on a regular basis, you can experience cleaner indoor air and fewer system issues.