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A man showing the different air filter sizes

Air Filter Sizes: What Size Air Filter Do I Need?

Walking down the aisle of your local big box home improvement store, you’ll find HVAC system air filters in a large variety of shapes and sizes. From basic, flat fiberglass filters to pleated box-type filters and everything in between, there is seemingly no end to the options. If you show up not knowing exactly what you need, there’s a good chance you’ll walk out with the wrong one. So, whether you are looking for the same filter size you always bought, or if you are replacing an air filter for the first time, understanding air filter sizes before you go to the store or start browsing online is the key.

Furnace and air conditioner filter sizes are relatively easy to figure out, but you’d be surprised how many folks just guess and get it wrong. Installing the wrong air filter size can damage the filter itself, cause inadequate filtering, restrict airflow, or reduce the life of the filter. On the other hand, correctly installing the right size of an air filter and replacing according to the manufacturer’s recommended schedule will help keep your indoor air cleaner and your system operating more efficiently.

That is why answering the question, “what size air filter do I need?” is so important. In this article we’ll cover why air filters sizes are so important, common filter sizes, how to locate sizing information and how to measure for a proper fit. When you’re done with this article and want to know more about air filters in general, check out our blog on the subject of “All About Air Filters.”

Why Are Air Conditioner Filter Sizes Important?

Most heating and cooling systems include some type of air filter, typically located within the indoor HVAC unit near the air circulating fan. Like its name entails, the filter “filters” airborne particles to provide two main benefits: improving indoor air quality and helping keep the HVAC system operate efficiently. Because furnace and air conditioner filter sizes can vary, it might be tempting to just get something that’s “close enough.” Unfortunately, this can lead to some issues, including:

  • If the filter is too small, it won’t catch all the air moving through the system and thus won’t filter out all the pollutants it was meant to catch. This can negatively affect the air quality inside your home.
  • An air filter that is too large will have to be forced into the filter compartment, which will damage the filter, meaning that air flow might be compromised, and you will have to replace the filter sooner. If a damaged filter severely restricts airflow, it may even increase your energy bills.

Remember, when you are shopping for filters, if you are paying attention to the MERV rating (you should be!) or any other performance metrics, the only way you’ll get the most for your money is by buying and installing the right size for your system. Installing MERV 13 (or the highest MERV rating your system allows without overtaxing airflow) and changing air filters on a regular schedule is the best way to continue maximizing air quality and system efficiency benefits.

Common Air Filter Size Chart

While there are a number of common air filter sizes, every HVAC manufacturer will have their own specific take on “standard sizes.” These might vary by a half-inch in thickness or more, depending on the brand. Length and width dimensions will also vary based on the size of the indoor unit and manufacturer. In some instances, you might have a filter bracket built right into the ductwork, which may call for a custom size not commonly available “off the shelf”.

The air filter size chart below shows the 1-inch filter dimensions that Carrier has available for purchase in either MERV 8, MERV 10, or MERV 13 from the comfort of home. Each pack coming with four filters and free shipping. If you’re not sure which MERV rating is right for you, please check out: What is a MERV Filter.

Once you have the right sized filter, and the right MERV rating, check out our blog regarding the steps to replace a filter if you need some tips on installing it.

What Size Air Filter Do I Need?

There are a number of simple solutions for answering the question, “what size air filter do I need?” Here are some examples: 

  • Assuming your existing filter is sized correctly, look to see if the dimensions of height, width, and depth are printed on its frame.
  • Look for the model number on your existing filter’s frame.
  • Look at the manual for your indoor unit and see if it lists the correct air filter dimensions.

A properly sized HVAC filter should slide easily into the compartment - you should not have to force into place.

Measuring Air Filter Sizes

If you can’t locate sizing information printed on the filter, or you believe your current filter is sized incorrectly, you can always resort to measuring the filter compartment. Using a tape measure, measure the length, width and depth of the compartment and write them down. Use these measurements to select your new filter.

You can confidently use your compartment measurements to select your new filter because manufacturers generally market air filter sizes using what is called their “nominal size” - the dimensions you’ll see listed on the filter packaging or store display. The actual size of the filter will be one-fourth to one-half inch less than the nominal size, so the filter should fit snugly within the compartment.

Shop for replacement filters from the comfort of your home and have them delivered to you for free, available from our product catalog.

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