Home Air Filter Sizes: How To Choose The Right Fit For Your HVAC System

Home Air Filter Sizes: How To Choose The Right Fit For Your HVAC System

If you have ever stood in the filter aisle wondering which size to buy, you are not alone. Home air filter sizes can be confusing, and getting the size wrong can hurt your HVAC performance, indoor air quality, and energy use.

In this guide, we walk through the most common home air filter sizes, what each type is typically used for, and how to measure your own filter so you can pick the right Aerterra filter size every time.

Why Filter Size Matters For Your Home

Your HVAC filter needs to do two things at once:

  1. Fit snugly in the filter slot so air is forced through the media.
  2. Allow enough airflow so your system can run efficiently.

A filter that is even a little too small can allow air to bypass around the edges, which reduces filtration and can pull dust into your ductwork and coils. A filter that is too thick or large for the slot can stress the blower motor and shorten equipment life. The EPA notes that properly sized and installed HVAC filters are a key part of improving indoor air quality in the home.

Nominal Size vs Actual Size

When you look at a filter label, you will usually see something like 16 x 20 x 1 printed on the frame. This is the nominal size, which is a rounded number used for shopping.

The actual size of the filter is usually a fraction of an inch smaller in each direction so it can slide into the filter slot. For example, a 16 x 20 x 1 filter might actually measure about 15.5 x 19.5 x 0.75 inches. Industry charts from major filter suppliers explain this difference between nominal and actual sizes and recommend measuring both your existing filter and the filter opening.

When you buy a replacement filter, match the nominal size printed on your current filter or on the filter cabinet.

Common Home Air Filter Sizes

Residential HVAC filters are measured in length x width x thickness, in inches. Here are some of the most common home air filter sizes in North America.

Common 1 inch filter sizes

These are the most common for standard residential systems:

  • 16 x 20 x 1
  • 16 x 25 x 1
  • 20 x 20 x 1
  • 20 x 25 x 1
  • 14 x 20 x 1
  • 18 x 20 x 1

Typical uses:

  • Single return grille filters in hallways or ceilings
  • Basic furnace and air handler cabinets in many tract homes and smaller systems

Explore compatible products:
Shop Aerterra 1 inch filters

Common 2 inch filter sizes

Two inch filters offer more surface area than 1 inch filters, which can support better filtration and longer life when the system is designed for them.

Typical sizes include:

  • 16 x 20 x 2
  • 16 x 25 x 2
  • 20 x 20 x 2
  • 20 x 25 x 2

Typical uses:

  • Systems with slightly deeper filter slots
  • Homeowners who want less frequent filter changes with a similar footprint

Common 4 to 5 inch media filter sizes

High capacity filters are usually 4 to 5 inches thick and are installed in a dedicated media cabinet on the return side of the furnace or air handler.

Typical sizes:

  • 16 x 20 x 4
  • 16 x 25 x 4
  • 20 x 20 x 4
  • 20 x 25 x 4
  • 16 x 25 x 5
  • 20 x 25 x 5

Typical uses:

  • Whole home media air cleaners
  • Homes that want higher MERV ratings and longer filter life
  • Systems designed for improved air quality and comfort

How To Find Or Measure Your Home Air Filter Size

If you are not sure what size you need, you can figure it out in a few minutes.

  1. Turn off your system for safety.
  2. Locate your filter. It may be behind a return grille or in a slot near the furnace or air handler.
  3. Check the label on the existing filter frame. Most filters have the nominal size printed along the edge, such as 16 x 25 x 1.
  4. If there is no label, measure the opening where the filter slides in. Use a tape measure and record the length, width, and depth of the slot.
  5. Round to the nearest whole inch to get the nominal size. For example, if the opening measures 15.6 x 19.4 x 0.9, you will usually buy a 16 x 20 x 1 filter.

What Different Filter Thicknesses Are Used For

1 inch filters

  • Most common in existing homes
  • Easy to find at hardware stores
  • Need more frequent changes, especially if you upgrade to higher MERV ratings

2 inch filters

  • More surface area than 1 inch, which can support better airflow at the same MERV rating
  • Often used when a homeowner wants better performance without upgrading to a full media cabinet

4 to 5 inch filters

  • Designed for high capacity media cabinets
  • Can support higher MERV ratings with less pressure drop compared to a 1 inch filter
  • Typically changed less often, which reduces waste and maintenance effort

Not every HVAC system can accept thicker filters, so it is important to check your manual or consult an HVAC professional before switching thickness.

How Filter Size Connects To Filter Performance

Size is only one part of the story. The other key factor is the MERV rating, which describes how effectively the filter captures particles of different sizes.

The EPA recommends using the highest rated filter your HVAC system and filter slot can accommodate, while still allowing proper airflow. Many homes start with MERV 8 as a default and can often safely upgrade, depending on the system design.

Choosing The Right Aerterra Filter Size For Your Home

Once you know your size and thickness, the last step is to choose the right Aerterra filter.

  1. Match your filter size
  • Use the nominal dimensions you found on your current filter.
  • Select the same length, width, and thickness from the Aerterra product page.
  • Example: If your label says 16 x 25 x 1, choose an Aerterra filter with that same printed size.
  1. Select your preferred MERV rating
  • Start with your system guidelines.
  • Many homes do well with MERV 8 or MERV 11 for a balance of airflow and filtration.
  • Allergy-sensitive homes may benefit from higher ratings if the system can handle it.
  1. Choose sustainable materials where possible

Aerterra filters are engineered with sustainability in mind, which helps you reduce plastic waste every time you replace a filter. Pairing the right size with a sustainable filter design means less bypass, better filtration, and fewer filters heading to landfills.

Explore options by size and MERV:

The Bottom Line On Home Air Filter Sizes

Choosing the right home air filter size is one of the simplest ways to protect your HVAC system and improve your indoor air quality. When your filter fits the opening, matches the correct thickness, and pairs with the right MERV rating, your system runs more efficiently and your home air stays cleaner.

Once you know your size, you are only a click away from a better filter. Ready to find your fit?

Shop Aerterra home air filters

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