Air Filters for Oklahoma Dust and Pollen: MERV Ratings and How Often to Change Them

The filter in your heating and cooling system is a small part that does a lot of work. It protects the blower motor and cleans some of the dust and pollen out of the air your family breathes.

Here is how to read the MERV number on the box, which filter to buy, and how often to change it.

What does a MERV rating mean?

MERV stands for Minimum Efficiency Reporting Value. It is a national rating for how well a filter catches particles, and a higher number means it catches more of them. The EPA says that for most particle sizes, a higher rating means higher removal efficiency.

Two numbers are worth knowing:

• MERV 6 and above. The U.S. Department of Energy says filters in this range can trap pollutants like pollen, dust mites and mold spores.
• MERV 13 and above. The EPA recommends at least MERV 13 if you upgrade, or as high as your system can handle. Filters at MERV 13 and above must show at least 50 percent removal of the smallest particles tested.

The Department of Energy also notes that a filter on the return side of the air handler protects the blower motor, so even a lower-rated filter has a job to do.

Which MERV rating should I buy for dust and pollen?

Start with what your system can handle, not with the highest number on the shelf. A denser filter is harder for the blower to pull air through. The EPA says most furnaces and HVAC systems can take a MERV 13 filter without equipment problems, as long as the filter is replaced often. It also says it can be hard to tell, because systems are rarely labeled with a filter recommendation, and that a technician can work out the best filter your system can use.

So the practical answer is:

1. If you are happy with your system and want better filtering, ask for the highest rating your system can take. For many homes that is MERV 13.
2. If you have not checked, ask a technician at your next visit.
3. If airflow seems weaker after a switch, call us and we will look at it.

Filters also come in different thicknesses, from 1 to 5 inches. Match the size printed on the old filter or in the slot. The EPA says the filter should fit snugly, so air does not leak around it and you do not have to bend or crush it to make it fit.

How often should I change my air filter?

Follow the maker's recommendation. The EPA says manufacturers typically recommend replacing filters every 60 to 90 days, and that many factors affect how fast a filter gets dirty. If the filter looks heavily soiled when you pull it out, change it more often.

A dirty or clogged filter can dramatically reduce airflow, which the Department of Energy says increases run time, wear on the motor and energy use. In summer that is the last thing you want from an AC.

Where is my filter?

The Department of Energy says the filter goes on the return side of the air handler. That means a slot at the air handler, or in a return grille when the equipment is somewhere hard to reach, such as an attic or crawlspace.

The Department of Energy says the filter should be somewhere the homeowner can get to. If yours is hard to reach, tell the technician at your next visit.

Does a better filter fix my dust problem?

Not on its own. The EPA says no filter removes every pollutant, and that filtering is a supplement to removing the source and bringing in clean outdoor air. Filters only work when the system is running. The EPA says most systems run less than a quarter of the time in heating and cooling season, and running the fan longer costs electricity and can make humidity harder to control in summer.

If dust is a constant problem, look at the ducts as well. Our post on signs your ductwork is leaking covers dusty air as one clue.

What if I want more than a basic filter?

Some homes add equipment beyond the filter slot. We install and service electronic air cleaners, media filters and Aprilaire purifiers, along with Air Scrubber and UV lights. See our indoor air quality page for what each one does. Before you buy any of them, ask what it adds over a good filter, and whether it gives off any ozone, which the EPA says to avoid.

Can you change my filter for me?

Yes. We change filters during tune-ups or on their own. Our maintenance page covers tune-ups and the membership, which includes fall and spring visits. If a storm has hit your system, our post on what to do with your AC after a hailstorm or power outage has the steps.

We serve Claremore and the towns around it. See our service area page for where we work.