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Time to get your MERV on: What is MERV rating?

MERV rating for allergies and sneezing

Why do we shut our houses up tight in the summer? Easy - when you're running the air conditioning around the clock, you don't want that precious chill sneaking out open windows or half-closed doors. Your whole-house lockdown makes the air filter in your air conditioner your leading defender against the allergens and mold spores that circulate around your home. And if you haven't thought about your MERV rating before, now is the time.

Understanding the MERV rating

MERV rating

MERV stands for the minimum efficiency reporting value (MERV) of the air filter in your air conditioning system. It rates the overall effectiveness of the filter— a higher MERV rating means finer filtration, so fewer dust particles and other airborne contaminants like pollen, dust mites, fibers, mold spores, pet dander and bacteria can pass through.

So the higher the MERV, the better, right?

While it’s true that a filter with a higher MERV rating lets fewer particles pass through, most home air systems work just fine with a MERV rating between eight and 13. Higher MERV ratings, in the range of 14 to 20, are typically found in hospital and general surgery settings.

What MERV rating do I need?

You may think you need a high-efficiency particulate arrestance (HEPA) filter to provide your home with the highest quality air available. Not always the case! A HEPA filter can be impractical in certain systems because of their density.

Also, if you install a filter with a lower MERV rating, more air is allowed to pass through, which may actually be a good thing for your HVAC system.

What’s important here?  Finding the appropriate filter with the correct MERV rating for your system and your home’s needs. Mike Brosselt of Angie's List notes that polyester and pleated air filters have a MERV rating between eight and 13 and will remove up to 45 percent of the air pollutants in your house.

High efficient air filters with a MERV rating 17 and above - "Often made from pleated filter paper or synthetic polyester fibers, high-efficiency filters can trap very small particles of dust, pollen, mold and other irritants" - may seem like a great idea, but Brosselt points out that the sacrifice in air flow can kill your HVAC system.

How often should I change my filter?

MERV rating

The basic answer to the question of when you should change the air filter is, “When it’s dirty.” You know it’s dirty when you can’t see the filter material through the accumulated dust. But how often should you check?

Consider these five factors:

  1. The type of filter your system requires
  2. The overall air quality where you live (Near a busy street? A factory? The rural countryside?)
  3. Whether you have pets, and how many
  4. How many people live in your home
  5. Whether any occupants have allergies

If you live by yourself, have no pets or allergies and there's not a coal-burning power plant in your backyard, you can probably change your filter about every six to 12 months. If you live in the suburbs and don’t have pets, check the filter every 90 days. If you have a single pet, you can check every 60 days.

Finally, if you have multiple pets or have allergies, you may need to change your filter every 30 to 45 days.

How do I replace my air filter?

In most home central air systems, you’ll find the filter in the blower compartment between the main body of the unit and the cold air return duct.

When you open the compartment door, pull the old filter out — slowly, to avoid contaminating the air — and insert the new filter with the arrows on the frame pointing toward the main body of the unit. Close the compartment door tightly.

For a window unit, you can probably just clean the current filter and reinstall it. Turn the unit off, then take off the front panel. You may have to use a screwdriver. You may also have to unscrew the filter itself to get it out.

After you shake or vacuum the dust off of the dirty filter, clean it gently with a combination of warm water and dish soap or white vinegar. Let the filter air dry completely before reinstalling it. If it has rips, holes, or other damage, it should be replaced.

Keep it cool, D.C.

Does your air conditioner need professional help? Schedule service with our experts in Washington, D.C., Northern Virginia and Maryland today. If you have questions about MERV rating or other general AC issues, feel free to drop us a note on Twitter @johncflood.