What MERV Rating should my filter be?

air filters

Changing your air filter is a vital part (though not the only one) of maintaining your home’s HVAC system.  As a consumer, when I go to the store to buy an air filter for my heating and cooling system, there are SO MANY choices!  If I wasn’t “in the know” it would be a little daunting.

 

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What Are MERV Ratings?

A trip through the filter aisle will bombard a shopper with all kinds of terms, which will naturally lead to some important questions! Some questions that can come up are:

What does “MERV” mean? What is a “pleated” filter? What is an “allergen” filter? What is an “electrostatic” filter? These are all great questions, and I will cover all that and more below.

First, it’s important to understand what your filter does: The common misconception is that the filter cleans the air in our homes and protects us from breathing in objectionable particulates.

While the filter does help improve the quality of the air inside the home, its actual purpose is to protect critical heating and cooling system components such as the evaporator coil, the blower wheel and motor and the compressor. Dust, hair, and other things in the air can clog up those important parts and reduce the heating and cooling capacity and efficiency and cause expensive repairs.
By filtering those things out of the air, and thus the heating and cooling system, it allows the system to work as the manufacturer intended. The fact that the filter also keeps those things from being recirculated is an added bonus.

So, who or what is MERV? MERV stands for Minimum Efficiency Reporting Value, which is a scale that goes from 1 to 20 (though in a residential setting we only go to 16). The higher the MERV value, the smaller the particulate, or object, the filter can catch.

As reported by the EPA, and reformatted on Wikipedia, below is what each MERV rating means:

MERV

Min. particulate size

Typical controlled contaminant 

Typical Application 

1–4

> 10.0 microns

Pollen, dust mites, cockroach debris, sanding dust, spray paint dust, textile fibers, carpet fibers

Residential window AC units

5–8

10.0–3.0 microns

Mold spores, dust mite debris, cat and dog dander, hair spray, fabric protector, dusting aids, pudding mix

Better residential, general commercial, industrial workspaces

9–12

3.0–1.0 microns

Legionella, Humidifier dust, Lead dust, Milled flour, Auto emission particulates, Nebulizer droplets

Superior residential, better commercial, hospital laboratories

13–16

1.0–0.3 microns

Bacteria, droplet nuclei (sneeze), cooking oil, most smoke and insecticide dust, most face powder, most paint pigments

hospital & general surgery

So now we know the “experts” say, but what does that really mean?  Well, here is that same list broken down a different way:

MERV

Type

Cost

1–4

Electrostatic, 1-inch Fiberglass

$

5–8

1-inch Pleated

$$

11–16

1-inch pleated, 4 – 6 inch pleated

$$$$

 

Since now we know what MERV is, and what it means, the next question is…

“Do I buy a pleated filter, an allergen filter or an electrostatic filter?”

Let’s take a look at each option below:

MERV 1 – 4

For the most part, these are your typical blue or white fiberglass filters.  They provide minimal containment and are designed to be replaced every month.  However, this MERV range also encompasses electrostatic filters.

An electrostatic filter is also known as a washable or permanent filter because it is designed to be washed and reused for years.  While this seems like a good idea at first, you should keep the following in mind:

  • Electrostatic filters have a low MERV rating (1-4), so do not do as good of a job filtering the air.
  • Needs to be vacuumed and washed every month!
  • Once properly washed, it needs to dry thoroughly before being put back in the system.
  • Can trap microbial growth inside, negatively affecting the air in the home.
  • These have the lowest cost, but also provide the least removal of dust and other particulates from the air.

MERV 5 – 8

These are the standard “pleated” filter.  The “pleats” on the filter give it more surface area to catch and collect dust and other particulates, and this type of filter can hold smaller particulates than a MERV 1-4 filter can.  A few things to keep in mind when buying these filters:

  • Higher cost per filter.
  • These filters begin to restrict the air that moves through the system and can cause noise at the filter intakes.
  • While they can last up to three months, I would recommend changing them every 1-2 months to keep them from causing issues with the HVAC system.

MERV 11 – 16

These are the best filters available residentially.  MERV 11 is commonly marketed as an “Allergen” filter and MERV 16 filters can filter out particulates as fine as cigarette smoke.  There is also more to keep in mind with these filters too:

  • Highest cost per filter.
  • Specialized installation – Most all MERV 16 filters are 4-6 inches thick and can only be installed in specialized filter compartments built into existing ductwork.  Adding this to existing ductwork can be expensive.
  • These filters can be highly restrictive to airflow and can cause issues such as freezing up and overheating in systems with inadequate ductwork or are not designed for such a restrictive filter.
  • These filters can last up to a year, but we recommend changing them every six months.

 

So, what MERV rating I use???

I know I’ve taken a while to answer the original question, but I wanted to give a better understanding of just what it all means.  The answer is, for most homes and most homeowners, the best furnace filters are in the MERV 5-8 range. 

If you, or others in the home have breathing challenges, or allergies to dust, pollen or other in-home irritants, moving to a MERV 11-16 filter can help combat the things that cause those allergies to flare up. We also have a full line of indoor air quality products that can supplement the homes filters and provide additional relief from allergies.

 

For a free, no obligation in-home consultation to determine what filtration system is right for you, please contact us!

 

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