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Is The Size Of Air Filters Important?

By enhancing the overall quality of the air you breathe inside your house, air filters do their best throughout the day and night to keep you as well as your loved ones safe. They take over the challenging responsibility of trapping allergens and dust particles to ensure that the air you breathe is fresh and healthy. However, a poorly fitting air filter stops it from performing its function correctly, leaving possibly harmful particles in the air that could have a negative impact on your health.

It is important that you think about the size of the air filter while exploring air filters and how they impact the quality of the air in your home. This blog will explain why the size of your air filter matters, how to find the right size for your home, and what can happen if you use a filter that’s the wrong size. A properly sized air filter makes sure your heating and cooling system operates efficiently and lasts a longer time,  along with helping to maintain clean air. In this blog, we will answer the question “Is the size of air filters important?” and give tips on choosing the right filter for your specific needs.

The Importance Of Air Filter Sizes

Air Filter Sizes

Maintaining clean indoor air quality and preventing the circulation of allergens and pollutants are the main objectives of air filters in your home. This is especially important for pet owners, who constantly find it difficult to manage pet hair. Although a lot of homeowners are aware that filters can enhance the quality of the air within the house, very few are concerned with the exact sizes of their air filters

Fewer people consider what might be the effects of choosing the incorrect size filter. Just like an outfit needs to fit you perfectly to look good while also functioning well, an air filter needs to be the right size to work effectively and provide the most beneficial results. Three key elements of an air filter to keep in mind are its size, the material it is made of, and its MERV (Minimum Efficiency Reporting Value) rating. 

The efficiency with which a filter can capture tiny particles can be determined by its MERV rating. Understandably, a higher MERV rating results in greater airflow resistance, but it also indicates better filtration. Finding the ideal ratio between material, size, and MERV rating is therefore important for keeping an air filter system functioning and secure.

Effects Of Choosing The Wrong Size Air Filter

Wrong Size Air Filter

For your HVAC system, picking the proper size air filter is important for a variety of reasons. There are more important things to consider in addition to making sure it fits properly. Let’s explore the reasons why selecting the appropriate air filter size is necessary.

1. Risk Of HVAC Damage – Aiming to fit an overly huge filter can result in damage to your HVAC system. It might not operate in the same way it previously did, or it could break down totally and demand costly repairs.

2. Trouble Closing The HVAC System – Your HVAC system will not be able to close correctly if your air filter is too big, as it will not fit into the filter vent properly. This could let contaminated, unfiltered air enter your house.

3. Poor Air Quality – Your HVAC system could find it difficult to keep up clean air if your air filter is not fitted properly, which could limit airflow. This can result in poor indoor air quality, which can lead to allergies, respiratory disorders, and other health risks.

4. Keeping Pollutants Out – If the size of your air filter is too small, some polluted air could still make its way through it and back into your house. This unclean air can cause health problems such as asthma or heart disease, which defeats the purpose of having an air filter. For this reason, it’s important to ensure that your air filter fits securely and without any empty spaces.

5. Higher Energy Use And Bills – Your HVAC system needs to function harder to remove pollutants from the air when you use the incorrect size filter. You are going to experience higher energy bills as a result of the extra work and more energy use.

Ways To Identify Your Air Filter Size

Label On The Filter Frame

You can figure out the size of your furnace filter in three different ways, which are mentioned below:

1. By Reading The Label On The Filter Frame

First, take out your current filter and look at the label on the frame of the AC unit to find out what size air filter you need. Most of the time, the label’s edge has the size displayed very clearly. It is important to remember that the clearly shown size is frequently only a rough estimate and might not be accurate. If the label fails to provide the exact measurements, you should measure the filter yourself to make sure the size you get is correct.

2. By Taking Measurements Of The Filter

If you are not sure about the size of your air filter, you can measure it yourself using a ruler or any measuring tool. Here’s how:

  • Before anything else, turn off your air conditioning unit for security reasons.
  • Measure the filter’s length, width, and thickness (depth) with the help of a ruler. As an example, consider the following measurements: 0.75 inches is the thickness, 24.6 inches is the width, and 15.5 inches is the length.
  • Calculate the nominal size by rounding all the measurements to the nearest whole number. For example: 1 inch is the thickness, 25 inches is the width, and 16 inches is the length. 
  • Check if the old size will work for your furnace before purchasing a new filter. Measure your air intake to ensure it is the right size for your system if you are unsure.

3. By Measuring Your Air Intake

If you intend to be sure that the filter you choose fits your system properly, measure the inside size of the air filter intake.

Here’s how to do it:

  • Turn Off Your AC – For the sake of safety, turn off your air conditioning system before you start measuring.
  • Measure The Inside Edge Of Your Intake – Measure the inside edge of the slot or frame of your air filter in terms of length, width, and depth using a measuring tape or a different tool.
  • Round Down – To figure out the nominal size of your air filter, round down to the nearest entire number. The slot or frame should be slightly bigger than the actual filter size, by around 0.25 to 0.5 inches.

Since measuring the air intake can be a little difficult and might not provide accurate measurements, it is still recommended that you try methods A or B in the beginning, such as checking the size of your previous filter or taking a direct measurement of the old filter.

Difference Between Nominal And Actual Filter Sizes

Nominal And Actual Filter Sizes

It is important that you understand the differences between nominal and actual filter sizes when choosing an air filter for your HVAC system. The filter package and frame have a notional size that is rounded to one decimal place; this is not the same as the exact measurement of the real size. A filter that is marked 20″ x 20″ x 1” may measure 19.5 x 19.5 x 1. The purpose of the difference is that the nominal size is rounded to the closest inch.

The nominal and actual sizes should be taken into consideration when selecting a filter. To figure out the real size you need, measure your filter slot first. Then, choose a filter whose nominal size is either the same as or a little bigger than the actual size. By doing this, you can be confident that the filter will fit your system properly and efficiently filter the air. It is essential to remember that choosing the appropriate filter for your HVAC system requires careful consideration of both the nominal and actual sizes.


Maintaining clean air inside your home and ensuring the proper functioning of your HVAC system depends greatly on the size of your air filters. In order to maximize efficiency and extend the life span of your system, choosing the proper size of filters is essential. The significance of having perfectly fitting filters is something we at Custom Filters Direct are well aware of. 

Our premium filters have been designed to increase efficiency and extend system life. Feel free to call us at 1-877-958-5612 if you require air filters. We are available to provide knowledgeable guidance and help you choose the correct filters for your house or place of work. You can count on Custom Filters Direct to maintain the excellent quality of air within your home and the effective functioning of your HVAC system.