Air Filter Buying Guide

Welcome to IAQ Filter Store's Filter Buying Guide.

What is MERV?

MERV stands for Minimum Efficiency reporting value. Simply put MERV represents the amount of particles a filter will remove from the air. For example the higher the MERV rating the smaller particles the filter will remove resulting in more pollutants being removed from the air. Most common Air Filters range from MERV 4 to 6 for your 30 day filters (Panel air filters) and MERV 8, MERV 11 and MERV 13 for your 90 day air filters (pleated air filters).

How do I choose an air Filter?

Different indoor air quality conditions calls for different levels of filtration. By knowing what the conditions in your home are and what your replacement air filter can remove will help you decide what type of filter do choose.

MERV 4 - Dust & Lint

MER 6 - Dust & Lint, Pet Dander, Dust Mites, Pollen – 30 day

MERV 8 – Dust & Lint, Pet Dander, Dust Mites, Pollen – 60 day Comparable to the Filtrete 1000

MERV 11 - Dust & Lint, Pet Dander, Dust Mites, Pollen, Bacteria, Mold – 60 day Comparable to the Filtrete 1500

MERV 13 - Dust & Lint, Pet Dander, Dust Mites, Pollen, Bacteria, Mold, micro allergens, smog, Virus ’– 60 day Comparable to the Filtrete 2200

Why does my Filter have two sizes listed?

Air and furnace filters have two dimensions. The first is the Nominal dimension. This is the general size of the opening the filter will fit into. The second dimension listed is the Actual dimension. This is the size of the filter if you were to actually measure the filter with a tape measure or ruler. The actual dimension usually has an undercut of ¼ to 1/8 of an inch smaller than the Nominal Dimension. This undercut allows the filter to slide into the track smoothly, without getting caught on the screws that hold the track into place.

For example a 20 x 20 x 1 air filter will have a Nominal size of 20” x 20” x 1 and an actual dimension of 19.5” x 19.5” x .75” .

Every Filter manufacturer has their own undercut so if you are looking for a special size, pay close attention to the actual dimensions.

How do I measure my filter?

Measuring your air filter is simple! Remove your existing, well fitting, air filter from your unit. Grab a tape measure. Measure the length, followed by the width and then the depth (thickness). In the Air filtration industry the Length is the smallest side, the width is the longest and the depth is the thickness.


Measure Short side for Length (L)

Measure Long side for Width (W)

Measure thickness for Depth (D)

Put your measurements together L x W x D


How do I know when to replace my air or furnace filter?

While most air filters for the home are designed to be replaced every 30 to 90 days. This number varies greatly depending on the conditions of your home, or the air in your community. If you live or work in an area with high chemical pollutants, or in an area with high allergens you may need to change out your filter sooner. Remember Jut because it doesn’t look dirty doesn’t mean it shouldn’t be changed.

Did you know … Changing out your air filter on a regular basis can save you up to $1.18 a day, on your heating or cooling bill, once your filter has become clogged?

If your HVAC system is constantly running or it never seems to be cooled off, check to make sure your air filter isn’t in need of a change out before you call your AC repairman.

What Does HVAC Stand for?

HVAC Stands for Heating, Ventilation and Air conditioning unit and refers to your central air and heating system in your home or business.