What is a MERV Rating on Filters?

Most folks don’t think about their air conditioner/furnace filters very often. In some cases they change their filters every month, sometimes every two months. If they’re like me it might be every six months. No matter how often you change it you should know that your air conditioner filter is an important part of the comfort of your home.

Without an air conditioner filter you not only jeopardize your air conditioner and furnace but you also allow impure air to circulate throughout your home. Yes, even though you may not know it, your central AC/Furnace also work as an air purifier for your home. That is what the filter is for. By changing it regularly you can continue that flow of clean air.

MERV Scale

But, how clean do you want that air in your home? This my friends is where the MERV rating comes into play. Filters are rated by quality under what’s known as the MERV scale. MERV stands for Minimum Efficiency Reporting Value. The MERV scale is a measurement of the percentage of particles that can be filtered out of your home. This scale can go all the way down to point-three microns up to ten microns. In other words, the MERV rating indicates just how much stuff you want your filter to catch. The higher the MERV on your filter the more particles you can trap.

A filter rated as a MERV one, two, three, or four are only rated to trap particles that are ten microns or higher. These are your basic filters that can trap some mold and pollen spores. The next step up are MERV ratings five through eight. These filters are significantly better and can trap particles as low as three microns in size. This can include the pollen and mold that we mentioned earlier but also forms of bacteria.

Now, if you were an allergy or asthma s sufferer then you will want to pay attention to the next few MERV ratings. These are the filters that are going to help you breathe easier in your own home. First, let’s look at MERV ratings nine through twelve. These filters can trap particles as low as one micron in size. These could include human or pet hair, dust, pollen, mold, and even combustion particles from fire places or candles.

The next MERV rating is between thirteen through sixteen. These ones aren’t as popular and can be harder to find but they can trap particles as low as point three microns. This will catch everything we mentioned above as well as cooking smoke, paint pigments, fungal spores, and everything else you can think of.

There is another category of filters that are rated as high as MERV seventeen through twenty. The catch here though is that these filters are known as ‘HEPA’ filters and they are the best of the best. You typically find these in hospitals or laboratories. They can be very expensive and you will also have to install a custom air conditioner/furnace system that can handle a HEPA filter. If you try to use a HEPA filter with a standard system then you risk overloading and eventually breaking your air conditioner/furnace. This is due to the thickness of the filter which causes your system to work overtime to push air through it.


In most cases I would recommend the MERV nine through twelve categories. This gives you a high quality filter and will provide you with clean air throughout your home. If you have a family member, or if you yourself, struggle with asthma or other allergies then you may consider the MERV thirteen through sixteen filters. In extreme cases a HEPA filter and system may be needed, but this can get quite expensive as you will have to get a non-traditional residential air conditioning system to support the HEPA filter.

If you find that you are a little overwhelmed with all of the choices out there then you can check out our Best Air Conditioner Filter guide. This guide goes through our recommended air filters in an easy to read ‘Good, Better, and Best’ category.