AC Air Filter Sizes

HVAC Measurement

At times, we don’t give air filters the respect they deserve.

From keeping indoor and outdoor contaminants out of our breathing air to keeping our HVAC system safe from any build-up, air filters have a more important role than we think.

HVAC companies advise users with indoor pets and a love for cooking to clean air filters every couple of weeks. This helps avoid filter saturation, requiring replacement and repair costs.

However, there may come a time when your existing air filter has outlived its purpose. Still, you can’t just run to the local hardware store to buy any sort of filter for your furnace.

There are a variety of filters you need to choose from! You can’t just fit a new air filter into any HVAC system.

How do you know which makes the right air filter for your HVAC system?

Learn more about HVAC filters and their sizes below.

Why Do Air Filters Have Different Sizes?

There are different filter sizes to fit various air vents. The ones you find inside air conditioners also differ from those integrated into air vents.

Air filter sizes matter because getting measurements wrong makes all the difference. For starters, the wrong size may mean leaving room for airborne particles to seep through vents.

To get the right filter, you need to get the exact dimensions of whatever you want it to fit into. Before buying those replacement filters, you should bust out your measuring tape and learn about the different filter sizes.

What Are the Standard Air Filter Sizes?

Below you will find examples of the most common air filter sizes readily available in most hardware stores. Their measurements match most air ducts and vent openings.

Remember, the closest possible measurement may only sometimes do the job. If nothing matches your old air filters, do not roll the dice on the closest available air filter.

If you have custom-sized air ducts, settling for the nearest inch is enough of a compromise. Here are the most common air filter sizes:

Common air filter sizes


  • 12 x 12 x 1
  • 14 x 14 x 1
  • 14 x 20 x 1


  • 20 x 20 x 1
  • 16 x 25 x 1
  • 16 x 20 x 1


  • 20 x 25 x 1
  • 16 x 25 x 4
  • 20 x 30 x 1
  • 20 x 25 x 4

You can get air filters to fit properly by getting those that share the exact size of the opening of your air vents. Don’t worry; some of these common air filter sizes may fit the exact measurements of your air vents.

Still, dedicate more time to measuring your vent twice. It will cost you less than buying new air filters twice. It also helps to remember that supply vents and return air vents have different sizes.

Do My Return Air Vents Need Air Filters?

Remember to measure both types of air vents to get different air filters for each. Yes, return vents need filters. They may not produce airflow, but they play their own role in facilitating it.

A clogged return vent can hinder your furnace. It may build internal pressure that counteracts proper air circulation. It will lead to hindrances in heating and surges in energy bills.

What Happens if I Get the Measurements Wrong?

You can say goodbye to decent air quality! Air filters play a specific role in your air conditioning.

An AC filter prevents particles from going around your indoor air and ensures the safety of your air conditioner. An integrated air filter helps protect your breathing air further while preventing risks against internal contamination.

A surplus of contaminants penetrating your air vents leads to poor air conditioning, impacting your home’s overall air quality and energy efficiency.

That’s right; filters are installed for your convenience in more ways than you think. Air filters protect you and your air conditioning systems from contamination to ensure seamless cooling.

Getting air filters in the wrong size may mean internal airflow contamination! That could spell disaster for your AC system. You may notice spiking energy costs and underperforming air conditioners.

How do filters impact your air conditioner’s internal components?

Internal components need protection, even when they are already encased within your indoor and outdoor units. You may keep your air conditioner off during winter, but it remains a dark and humid environment for unwelcome inhabitants.

Creepy crawlies and bacteria may seep into its components without the right filter to keep contaminants away. That ought to be a treat for your family in summer…if your air conditioner starts up at all!

Enough particle pollution and contamination may render your air conditioner unusable. Getting the right AC filter sizes is vital for you and your AC unit.

How Do I Measure My Air Conditioner’s Vents to Get the Right Filter Size?

Finding the right air filter sizes is easier than you think. You can always use a measuring tape to measure things end-to-end or the filter frame of your existing filter.

However, your home’s air filter should indicate its measurements on one side of its frame. You will see its exact length, width, and depth measurements.

We know what length and width measurements are, but you should remember another important measurement. Depth measurement pertains to how thick it is.

Thickness matters! Thicker filters have more filtration and last longer than thinner alternatives. Here’s an idea to compare the two:

A thin air filter needs changing or cleaning at least once a month. AC filter sizes range in depth measurement, but you may find ones up to four inches thick. A thicker filter can last twice as long as a one-inch filter.

What’s the Difference Between Nominal Size VS Actual Size?

Fortunately, there isn’t much of a difference between the two. The nominal size is based on the ACTUAL size of the air filter. However, the nominal size is a rounded estimate of the actual sizes.

Your furnace filter sizes may also have nominal length, width, and depth values. If the new air filter’s nominal size matches your old ones, they make viable replacement filters.

If your AC filter size is wrong, you may notice a few things with your cooling system. That airtight seal means the difference between high-quality air and higher energy bills.

What’s Wrong with My Air Filters?

Remember, enough wiggle room means higher chances for more particles to contaminate your air conditioner or indoor environment. Apart from buying the right filter size, there are other things you must always consider.

Filter size is just the beginning. Your AC requires clean, fit, and adequate air filters. What do we know about MERV ratings?

What is a MERV Rating?

A Minimum Efficiency Reporting Value (MERV) Rating indicates how efficiently air filters can screen airborne particles. We already know an air filter can impact your energy costs, but they do so in more ways than one.

An air filter with higher MERV ratings can sift more particles out of indoor air better than some. They may filter particles up to as small as .3 microns.

Remember, more particles that make it through the air filter can contaminate your air conditioner. Your air filters with high MERV ratings can protect your ductwork, vents, and air handlers from dust mites crawling into their blowers and chambers.

Choose an AC filter with a MERV rating of at least 8 to 10. A MERV rating higher than ten is great but unnecessary. Any lower than eight, and you may have to replace your filter every other week.

If you have a few extra dollars to spend on air filters, spring for a MERV rating higher on the numerical chart.

How Often Should I Replace My Air Filters?

Most air filters can go without replacement for more than 60 days. Still, some filters can only withstand up to 14 days of continuous exposure.

How often you should replace your air filter depends on three things:

  1. What type of air filter you have at home.
  2. The condition of your Indoor Air Quality.
  3. How often your HVAC systems undergo maintenance and tune-ups.

The latter two take more evaluation to answer. However, we can help you with the first number on the list.

The Different Kinds of Air Filters

The most common integrated filters in homes across the U.S. are pleated and spun fiberglass. Which air filters do you have?

Pleated Air Filters

Pleated filters are synthesized fabric. They can filter smaller particles with more efficiency. They can withstand pollution and remain efficient for up to 60 days of exposure.

They are a little more expensive than affordable alternatives but are more low maintenance than most of their counterparts.

Fiberglass Air Filters

Fiberglass air filters are made of spun fiberglass. They are inexpensive and come in various filter sizes. However, they are reportedly flimsier. Most fiberglass filters are often discarded due to bent corners and saturated surfaces.

They may only last up to 30 days and are more noticeably saturated than more expensive alternatives.

Preventive Maintenance

An air filter is primarily disposable. You can recycle or reuse them a few times. However, they don’t have an infinite lifespan. They will outlive their use after a few washes.

Still, it would be best if you didn’t underestimate the power of preventive maintenance. Routine cleaning and tune-ups help most HVAC system components. It helps boost your entire AC and furnace.

While you should keep an eye on your air filter and replace it whenever it gets dirty, enlisting professional cleaning for your AC system can lessen their burden. You should always check your systems before they start stalling!

Do You Need Professional HVAC Services in Puyallup, Washington?

You may have overlooked the condition of your air conditioner for too long. It may have already contaminated various internal components.

If you have already tried replacing your air filter and still experience hindrances in heating or cooling, you might already have more worrisome HVAC problems.

Get in Touch with Taylor Heating & Air Conditioning Today!

We can do more than replace your air filter with one in the right size! We offer maintenance, tune-ups, and repairs!

Taylor Heating & Air Conditioning can help you with Air Conditioner Repair and Furnace Repair in Puyallup, Washington.

You can also call us for AC Installment & Replacement and Furnace Replacement & Installation Services.

Leave Us a Message at (253) 785-9194 or Call Us for Emergency HVAC Assistance at (253) 208-5315

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