Choose the Right MERV-Rated Furnace Filter for Your Needs

March 23, 2020

Furnaces have air filters in them, and these filters are rated according to a minimum efficiency reporting value (MERV) scale. This scale escalates from MERV 1 to MERV 20, with the higher numbers corresponding to better air filtration. Here's how to select the right MERV-rated furnace filter based on your air quality needs.

MERV 1 to 4: Minimal Filtration That's Unsuitable for Furnaces

Filters with ratings between MERV 1 and MERV 4 only offer minimal filtration. They'll filter out pollen and dust mites, but they'll miss small particles that you don't want in your home. For example, these filters don't catch mold spores — so mold would be free to circulate through your home's heating system if you used this basic a furnace filter.

MERV 1 to MERV 4 filters are commonly used on window air conditioning units, and they're suitable for this application. The filters will catch any pollen that a window air conditioner might let in, and mold generally isn't a problem because these units don't recirculate air around the house.

For a furnace, however, these filters aren't suitable. They'll let many airborne particles pass throughout your house, and those particles could remain in your house for a long time since you probably don't open the windows to let fresh air in very often when you're running the furnace.

MERV 5 to 8: Decent Filtration That's Appropriate for Many Furnaces

Furnace filters rated between MERV 5 and MERV 8 are typically suitable for homes where there aren't special considerations (see following sections), and this is probably where you should begin your search for a good filter. For many homeowners, any filter in this range provides adequate air filtration.

Importantly, filters in this range will trap household products like hairspray and organisms such as mold spores. Thus, both cosmetics that family members use and potentially harmful living pollutants will be stopped from getting back into your home's rooms once they enter the furnace's air stream.

MERV 9 to 10: Superior Filtration That's Good for Most Homes

If you want superior air filtration but don't have any specifically identified need for the added filtration, a MERV 9 or MERV 10 filter might be a good choice. Both of these provide superior filtration.

Specifically, filters with these ratings begin to remove particles that measure between 1.0 and 3.0 microns in size. A MERV 9 filter has an arrestance of >90%, and a MERV 10 filter has an arrestance of >95%. MERV 8 filters don't remove particles that are this small but still has an arrestance of >90%.

MERV 11 to 13: Excellent Filtration That's Good for Allergies 

If someone in your home suffers from allergies, a MERV 11 to 13 filter will help remove allergens (including pet allergens) from the air. These filters are the best ones that still commonly get installed in residential settings.

If you're in a home that has an allergy sufferer and someone who smokes, go with a MERV 13 filter. Not only does a filter with this rating remove allergens, but it also takes some tobacco smoke out of the air. 

Because these filters are much more effective than other furnace filters, they might cost more. The added cost, however, is a small price to pay if the filter helps one of your family members suffer from allergies less.

MERV 14 to 20: Outstanding Filtration for Non-Residential Settings

There are still better filters available, but these aren't used in residential settings. 

Filters with MERV ratings of 14 or higher are installed in hospitals and industrial buildings. MERV ratings up to 16 might be used in surgical centers, while those with MERV ratings between 17 and 20 are reserved for pharmaceutical manufacturing, buildings with radioactive materials, and cleanrooms.

If you need a furnace filter to improve the air quality of your home, contact Service 1 Plumbing, Heating & AC, Inc.