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Buying Furnace Filters? 3 Things You Need to Know

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airfilterIf you are out of furnace filters and looking for new ones, it’s easy to get overwhelmed by all the choices. But be diligent. The filter you buy strongly affects your:

Here are 3 things you need to keep in mind to find the filter your furnace needs.

1) Know the size you need

This sounds like common sense. But you don’t want to assume you know the size of your filter only to come back with the wrong size. 

Look on the edge of your current furnace filter, and you should see 3 numbers. Example: 14 X 25 X 1.

These numbers, respectively, are the:

  • Height
  • Length
  • Thickness/depth

Make sure the filters you buy match the size of your current furnace filter.

2) Understand the MERV rating

Furnace filters have a MERV (minimum efficiency reporting value) rating. This rating, ranging between 1-16, determines how efficient the air filter can catch allergen particles.

The MERV rated filter you get depends on these 2 factors:

  • Allergen needs– Do you have someone in your home with allergies? Then you’ll want a higher MERV rated furnace filter.
  • Budget– More efficient filters cost more money.

We’ll explain which furnace filters relate to each MERV rating and what each rating can filter out in the next section.

3) Know your furnace filter options

There are 4 main types of furnace filters:

Fiberglass furnace filters

MERV rating: 1-4

  • Cheapest furnace filter ($1-2)
  • Does not block airflow
  • Good for renters


  • Does not catch smaller particles that hurt those with allergies and asthma issues
  • Need to replace often—every 30 days or so.

Pleated furnace filters

MERV rating: 5-8

  • Relatively inexpensive ($4-5)
  • Has a larger surface area so it catches smaller particles like spores and mites


  • Adds more resistance to airflow. This causes the furnace to run longer, making it more expensive to use, and hurts the furnace in the long run. 
  • Needs changing frequently or the airflow blockage gets worse

Electrostatic furnace filters

MERV rating: 9-10

  • Uses self-charging electrostatic cotton or paper fibers to attract and trap small particles, so it can catch smoke particles and pet dander.
  • Great for families with pets and children, and smokers


  • Can get expensive over time, especially for custom sizes

Air cleaners

MERV rating: 12-15

  • Most efficient filter you can get; removes particles as small as 0.3 microns, including bacteria, mold, mildew and smoke particles
  • Perfect for those with serious allergies and asthma symptoms
  • Only needs annual maintenance


  • Most expensive option
  • Needs a professional to install and maintain

What we recommend

We recommend standard fiberglass filters for most home owners and the air cleaners for those with serious allergies/asthma.

Why air cleaners and not pleated filters? Pleated filters restrict airflow, increase your energy bills and can ruin your furnace by making it run longer. Plus, they can’t catch nearly as many harmful particles as air cleaners can.

Want to learn more about the furnace filter you need? Talk to one of our experts.

Air Professionals is a whole-home comfort company serving New Jersey homeowners. Contact us for more information on how we can help improve your home’s comfort.