Furnace Filter 101


As we all shelter in place one of the things that will matter most to all of us is the quality of our indoor air. This is especially challenging for children with asthma and other at-risk populations with respiratory concerns. With COVID-19 in the area, this is of particular concern.

If you are like the vast majority homes in West Michigan and have a forced air furnace, one simple thing you can do to dramatically improve the air quality in your home is to regularly replace your furnace filter.

The most common type of furnace filter is the disposable pleated kind. These come in a range of standard sizes and ratings. Pleated filters are constructed out of paper and polyester and do a good job at filtering most household particles and allergens.

Furnace filters are sized by thickness (depth), height and length. To find out what size filter your furnace uses, remove and check the old filter, the size should be written on the frame of the filter.  You can also refer to your furnace manual.

What’s a MERV and why should you care?

Furnace filters are rated using a MERV (minimum efficiency reporting value) rating. MERV ratings range from 1 to 16.  Higher MERV ratings capture smaller particles.

The Healthy Homes Coalition recommends a minimum of a MERV-8 filter to filter out allergens, pollens, irritants and bacteria for better lung health. A MERV-8 filter, however, will not filter out the coronavirus (more on this below).

How often should you change your furnace filter?

Once you know what size filter you require and what MERV rating you can use, and have chosen what filter type to purchase, it’s time to replace the old filter. On many furnaces, you can see the furnace filter between the air intake and furnace itself. Some furnaces may have a compartment door over the filter. Simply slide the old filter out and properly dispose of it. Often it will be dusty, so try to place it in a bag as quickly and gently as possible. Your filter should be replaced every 90 days at a minimum.

NOTE: To ensure your furnace doesn’t kick in while you’re changing your filter it’s recommended you turn your furnace off while swapping out the filter.

That’s it. Now you are ready to enjoy cleaner, healthier air at home!

Air quality and COVID-19

Many people are concerned about the airborne spread of the coronavirus. While this is a possibility, it should be noted that airborne transmission is usually though large droplet transfer, which the Center for Disease Control (CDC) puts at about six feet.

Smaller particles are possible, and if those droplets get into the air intake of your heating system, a MERV-13 filter may be your best defense. However, there has not yet been conclusive research about the effectiveness of furnace filters in filtering out the coronavirus. Furthermore, your furnace may not operate correctly with a highly efficient MERV-13 filer, so please check your manual.

It should be noted that there are many other ways in which the coronavirus is spread, including surface transfer and coming into contact with infected persons. With that in mind, running to the store to purchase a high-efficiency filter may put you at greater risk than using your existing filter.  Instead, put a furnace filter on your shopping list for the next time you have to go to the store, and pick up more than one so you have replacements on hand.

Our reason for sharing this information on furnace filters is not to suggest that they will keep you safe from the coronavirus. What a clean, MERV-8 furnace filter will do is improve your overall indoor air quality to remove allergens, pollens, irritants and bacteria to help to keep asthma better managed. It will also improve general air quality for all.

Check out our video below!