MERV Ratings: What to Know When You Shop for Air Filter Replacements

March 21, 2014

Furnace Filter

Whether the HVAC systems in your Ocala area home include a furnace, air conditioner or heat pump, regular air filter changes are essential for keeping your system clean and operating efficiently, and to keep your energy bills in check. A dirty air filter is one of the most common causes of HVAC problems, and can lead to system failure. Understanding MERV ratings can help you choose the best filter for your system.

The Purpose of Your HVAC Air Filter

Your air filter serves two critical functions for your HVAC system:

  • It protects your system from dust, which can overheat the system and damage the essential components, leading to costly repairs and even replacement.
  • It cleans your home’s air to improve your indoor air quality. Your air contains numerous particles, including mold, pollen and dust mites,

A dirty air filter allows dust to build up inside your system, leaves more contaminants in your home’s air, and restricts airflow to your furnace or air conditioner, which can cause the equipment to overheat and fail.

How Often Should You Change Your Air Filter?

The air filter may need to be replaced every month or every two or three months, depending on where you live, the size of your household and whether you have pets. Experts recommend that you inspect your air filter every month and replace it when you can’t see the filter material through the dust.

How to Determine the Size of Air Filter

Refer to the specifications of your HVAC system to determine the size of air filter it requires. Additionally, you can simply look at the old filter. The dimensions should be printed on the frame.

Air Filter Choices: MERV Ratings

Air filters vary considerably in quality. The MERV scale is a standard measure of the ability of a filter to remove particles from your home’s air. MERV ratings range from 1 to 20, with lower ratings denoting a lower-quality filter.

  • MERV 1-4 Filters: Filters with a MERV rating of 1 to 4 do little to trap harmful particles in your home’s air. They are flat instead of pleated, which means there’s less area for trapping a larger number of particles. Additionally, they only trap particles larger than 10 microns, such as pollen, dust mites and carpet fibers. The main purpose of these filters is to give your system minimal protection against dust, and they need to be replaced more frequently than higher-quality filters.
  • MERV 5-8 Filters: MERV ratings of 5 to 8 indicate a medium-quality filter that’s sufficient for most homes. They trap particles as small as 3 microns, which include mold spores, animal dander, and the highly allergenic droppings of dust mites.
  • MERV 9-12 Filters: The U.S. Environmental Protection Agency advises that filters with MERV ratings of 9 to 12 are almost as effective as true high-efficiency particulate absorption, or HEPA, filters when it comes to removing particles from indoor air that are hazardous to your health, which makes them ideal for homes with occupants who have COPD, allergies, asthma and other respiratory conditions. These high-quality filters trap particles as small as one micron, including Legionella and humidifier dust. MERV 9 to 12 filters are the best filters that a residential HVAC system will accommodate without serious system modifications.
  • MERV 13-20 Filters: These exceptional filters, which can trap viruses, bacteria and carbon dust, are usually used in commercial HVAC systems, such as those in manufacturing operations or hospitals. A residential system will not accommodate filters with MERV ratings above 12 without modifications (unless it’s previously been retrofitted for a higher-efficiency filter).

Balancing Air Cleaning With Air Flow

A dirty filter can damage your system by restricting the flow of air, but so can a clean filter that’s too dense for your system. It’s essential to check the specifications of your system before upgrading your filter to a higher MERV rating. You can also ask your HVAC technician for recommendations during your annual preventive maintenance call.

How to Replace Your Air Filter

In most systems, the air filter is housed in the blower compartment, between the air return and the furnace or air handler itself. Have a plastic bag handy to put the dirty filter in, since the particles it contains are very small and can become airborne quickly. Open the compartment door and slowly remove the dirty filter. Insert the clean filter with the arrows printed on the frame pointing in the direction that the air flows, which is away from the air return and toward the main unit.

For more advice about how to choose the best air filter for your Ocala area home, please contact us at Sun Kool Air Conditioning, Inc.

Image Provided by Shutterstock.com

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