What Size Air Filter Do I Need For My HVAC System?

Presidential Heating & Air Conditioning

Gaithersburg HVAC Contractors


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The air filter in your HVAC is the component that keeps dust, animal hair, and other airborne particles out of your HVAC system. As a result, the air filters are important in prolonging the life of your HVAC system. Knowing the proper size air filter needed is beneficial to your system’s lifetime. Protecting your HVAC equipment is the primary purpose of an air filter.

Air filters can improve the quality of the air inside your home. Air filtration occurs when the air is circulated through your home and brought back through your air ducts into the HVAC equipment to be heated or cooled. Then it is recirculated. During this circulation process, your HVAC system pulls the air through the air filters, and the filter removes particulates from the air.

Man replacing Air FilterLike the air filter in your vacuum cleaner or in your car, dirty HVAC air filters need to be replaced regularly. Disposable air filters are available in most home improvement stores. They consist of layers of fiberglass or pleated paper, and they are rimmed with cardboard available in various densities, shapes, and sizes. Some HVAC systems use air filters that do not need to be replaced. These systems have air filters that can be cleaned, dried, and reused.

Size and Type of Air Filter You Need

The size, efficiency, and type of air filter your system needs depend on your system.


In most HVAC systems, you can find the air filter in the return air duct. Look for a grill or box cover on a wall near the furnace, or in some cases inside or on the air handler itself. The air filter size should be exactly the same size as the frame around that opening, or incrementally smaller. It is very important to use the right size air filter because a wrong-sized filter is the same as having no filter at all, which can damage your HVAC equipment. If you are unsure of the size, remove the old air filter and you will see the size stamped on the edge of the frame.

If you measure the filter yourself, your measurements may not match the measurements on the filter label. For example, you may measure the filter at 19 ⅝” x 19 ⅝” x 13/16” but it will be labeled as 20 x 20 x 1. Note that most filters are 1” thick, though some systems will use thicker filters.

The most common furnace filter sizes are 10 x 20, 14 x 20, 16 x 24, 18 x 30, 12 x 12, 14 x 24, 16 x 25, 20 x 20, 12 x 20, 14 x 25, 18 x 18, 20 x 24, 12 x 24, 14 x 30, 18 x 20, 20 x 25, 12 x 30, 15 x 20, 18 x 24, 20 x 30, 12 x 36, 16 x 20, 18 x 25, 4 x 24, and 25 x 25. However, there are over 75 different standard filter sizes.


Air Filter ReplacementBe careful when selecting a high-efficiency air filter. It is true that not all air filters will clean your indoor air to the same degree. Higher-quality filters cost more and will remove smaller particles, but they will make your HVAC equipment work harder.

You can tell what level of efficiency an air filter offers using the filters’ “minimum efficiency reporting value,” otherwise known as the MERV rating. Standard MERV values range from 1 to 16, with the number serving as an indicator of how well the filter will remove pollutants from the air. Higher MERV numbers indicate better filtration.

  • MERV 1-4: These are common standard filters that provide a basic level of filtration at a low cost.
  • MERV 6-8: These filters provide good filtration and are commonly used in residential settings.
  • MERV 9-12: Mid-range filters like these are of relatively high quality and can capture very small particles of 1 micron or larger.
  • MERV 13-16: These high-efficiency filters are the best standard filters available. They can remove very small particulates of 0.3 microns or larger.
  • MERV 16+: These high MERV-rated filters are very thick and dense. They can obstruct the airflow through your HVAC equipment with adverse effects if your system is not designed to handle them. For example, extremely high MERV filters can reduce your heating and cooling effectiveness and overburden its components. Restricting the airflow in your system could damage it in the same way that using very dirty filters can. Consult with a professional HVAC technician before you install a high MERV filter.

Use Clean Air Filters

Air FilterKeep in mind that whenever your HVAC system is running, it will circulate all the air that heats or cools your home through the air filters in the HVAC system. Using clean air filters in the system is one of the least expensive ways to maximize the life of your equipment. Dirty, clogged air filters are one of the main causes of HVAC system breakdowns because dirty air filters can reduce the airflow inside the HVAC system, which can cause air-handling fans to work harder, use more energy, and wear out faster.

How do you know it’s time to change the air filter? Some typical signs you need to change your air filter include the following:

  • Look at the old filter. Change it if it is noticeably gray in color and you can see dirt and dust build-up on the filter media.
  • You notice that your home is dustier than usual.
  • Your heating or cooling system is running longer or more often than it usually does.
  • You have not changed (or cleaned) the air filter in more than sixty days, or it has been in use longer than the manufacturer’s recommendation.

Contact the Experts at Presidential Heating and Air Conditioning for More Information

You can actually damage your HVAC system if you use the wrong air filter. Be sure you are getting exactly what you need by consulting with the HVAC professionals at Presidential Heating and Air Conditioning. They can answer any of your questions regarding air filters, and they can schedule an appointment for one of their technicians to perform an HVAC evaluation for you. They can service your system if needed.

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