The ABCs of the Best Furnace Filters

Published by 
AllThingsHVAC
Last updated: 
March 13, 2024

What do you usually think about when you read “MERV”? You’ll be surprised to find out it’s an ancient city in Turkmenistan, as well as a game show on TV. But most importantly, it stands for Minimum Efficiency Reporting Value. This standard system enables customers to make a comparison between the filters produced by various manufacturers. The values can range anywhere from 1 (which represents the lowest efficiency level) to 20 (which stands for the highest efficiency level). Based on your needs and budget, when choosing a filter you should also keep in mind what particles you want to trap and how often you’ll have to change the filter.

How furnace filters work

Best Furnace FiltersBesides protecting the furnace, filters also help us keep allergens and contaminants away by constantly cleaning the air that circulates through our homes. A furnace filter’s efficiency level varies. In a nutshell, forced-air furnaces draw air in order to heat it before pushing the air into the rooms via ducts. The same process applies during the summer when you turn on your air conditioning, with the only difference that the air is being cooled down. A furnace filter’s job is to prevent dust, hair and other contaminants from being sucked into the fan. A dust free motor will live longer and won’t break down within a few months. If, in the early days, furnace filters were designed to protect the internal parts of the fan from being overwhelmed by dust and other gunk, the focus of their use has shifted in time. They’re now used to keep us healthy and safe from allergies and bacteria.

Filter types

The most popular kind of filter is the disposable pleated one. You can find it in various sizes and qualities. These are made out of paper and polyester and will do a good job at trapping the vast majority of particles and contaminants. Pleated polyester filters will last up to three months and are able to attract small particles to keep the air in your house clean. Fiberglass or cellulose pads are the cheapest alternative, but what you get is what you pay for. They’re set in a cardboard frame and will only catch big particles that can damage your furnace. Reusable filters can be washed and used over and over again for up to five years.

The plastic or metal foil pad they use can be coated in a material that will help them increase their efficiency of trapping smaller particles. Deep pleated air filters are four to six inches thick. This makes them difficult to set in the standard holders. These are highly efficient air filters made from one hundred percent synthetic media. Finally, electronic filters require a special box to be installed in the duct system. They run on electricity and trap the smallest particles to a negatively charged element. Electronic filters should be washed regularly, once a month. They are the most efficient, but they’re also expensive to fix or replace.

Merv ratings overview

Furnace filters are no longer a whim, they’ve become a necessity. As our air becomes more and more polluted, we need to make our homes a safe environment. There is a great variety of air filters out there that can suit all expectations. Let the system rating guide you when you’re making your choice. The higher the Merv number, the better the filter will do its job of trapping small contaminants. Merv 1 to 4 are used most of the times in residential buildings. Because they offer minimum filtration, they remove less than twenty percent of the 3.0 - 10.0 particle size microns. With these types of filters you’ll get rid of pollen, dust mites, spray paint dust and carpet fibers. Opting for permanent, metal and foam Merv 1-4 filters will keep you within the budget, but it won’t thoroughly protect you against contaminants and allergies.

On the other hand, Merv 5 to 8 filters are better suited for residential buildings and industrial workspaces. Merv 8 filters do a much better job at protecting you from mold, spores, and dusting aids. Their efficiency level varies between twenty and thirty five percent. If you opt for one of these you’ll have to replace them every sixty to ninety days. Merv 9 to 12 are some of the best furnace filters. They trap between fifty and eighty nine percent of particles, including lead dust and milled flour. The next Merv ratings vary between 13 and 16. These will catch tobacco smoke, bacteria and proplet nuclei (sneeze) with efficiency levels going as high as ninety five percent. The highest Merv values range between 17 and 20. Most of the times, these filters are used in hospitals, general surgery rooms and health care buildings.

It’s important to choose the best furnace filter that will strike the perfect balance between cost and efficiency. By implementing a highly efficient furnace filter you risk slowing the airflow to a great extent, but low efficient filters will fail to trap small particles that become dangerous in the long run. Merv 8 and Merv 11 filters are a justifiable investment and the best choice for families with kids, pets and asthmatics.

Merv 8 filter specifications:

  • Furnace Filter Typeshigh end type of filter;
  • perfect choice for families with no asthmatic members;
  • capable to trap fabric protector, hair spray and dust mite debris;
  • carbon activated Merv 8 filters protect against odors (cigar smoke, pets odor);
  • filtering effiency between 70%-85%;
  • change frequency ranges between 60 and 90 days;
  • suitable for any type of installation.

Merv 11 filter specifications

  • high end type of filter;
  • superior air filtration, eliminating bacteria, mild and pet dander;
  • ideal choice for people that have several allergies, respiratory difficulties or asthma;
  • can filter out over 85% or 3.0 – 10.0 microns (including humidifier dust and auto emissions);
  • compatible with any kind of installation;
  • recommended to be changed oncer every two or three months.

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