The minimum efficiency reporting value or MERV rating, is used to rate the effectiveness of air filters. The rating system was designed by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) in 1987.
Cheaper filters won't trap as many particles & need to be changed more often …
The MERV rating represents the worst case performance when removing particles that range from 0.3 to 10 microns, which are sizes we can't even see. These particles include dust, pet dander, pollen, dust mites, carpet and textile (clothes) fibers, mold spores, bacteria and smoke.
Picking the Right MERV Rating
The scale for MERV ratings goes from 1 to 16, with higher ratings indicating a higher percentage of particles captured. At the high end, a filter rated at 15 will capture 95% of particles.
But … a higher MERV rating isn't always better. The higher the MERV rating, the smaller the pores are and less air will flow through your the filter. This resistance in airflow can make your furnace or air conditioning system run longer, which will increase your operating costs. So you want to do some research to find the highest MERV rating that will let your system run efficiently.
Typical filter ratings used are:
- MERV ratings from 7 to 12, are used for homes.
- MERV ratings of 13 to 16 are most often used in hospitals and sensitive manufacturing environments.
When Should You Change Your Filters?
Now that you understand how air flow affects the efficiency of your heating and cooling systems, you should recognize that a dirty filter will also restrict air flow. So the trade-off is paying to replace your air filters to reduce your heating/cooling bills, or face higher utility bills.
You'll need to do some research to determine the ideal MERV rating for your HVAC system. Once you've done this, write down your rating and filter size (mine is 20 x 30 x 1 in) on a mailing label, and stick it on the filter frame where it's easy to find.
The real challenges are remembering to change your filter(s), and buying them. A great solution I've found is setting up automatic deliveries or an Amazon subscription (learn how Amazon subscriptions work, including an opportunity to earn a discount). You may prefer shopping at FilterBuy.com as they make it easier to find your filter size with your desired MERV rating. Shipping is free and they also have a subscription service.
PS Prices are about the same on Amazon and FilterBuy and you can even get FilterBuy filters … on Amazon!
Check the size of your current filter which hopefully is the correct size … but not always. I was amazed that the HVAC install team for my new home shoved a filter in that was two large for the opening, which made it difficult to remove. Fortunately I knew it was just cardboard really and relatively inexpensive, so I tugged until it came out.
If you want to check the measurements of your filter and the opening, understand that a 20 inch filter is a quarter inch less … giving you wiggle room to slide the filter into position.
Ready to order your filters? Many home experts will tell you to change the filter every month and I have some friends who like following directions. At the same time, I know that depending on where you live, your HVAC system might only run six months out of the year so you don't have to change the filter during these “off” times. Filters with higher MERV ratings also have more surface area, so they don't have to be changed as often.
- Filter size which varies quite a bit (mine are 20 x 30 x 1).
- MERV rating (8, 11 or 13) you want.
- Schedule for changing your filters, e.g. I want to change mine once a quarter.