AC/Furnace Filters, Allergies, & Asthma

Suffering with asthma can be a horrible experience. Depending on the person’s triggers they may be outright excluded from certain things or from even going outside during certain times of year. My father, for example, cannot set foot in a home that has a cat in it… or that had a cat in it twenty years ago. It doesn’t seem to matter how long ago it was. His asthma will still get triggered by stray cat hair floating through the home. In many cases it will get so bad that an inhaler is needed. Then, even when the worst of the symptoms go away, he will be recovering for days to come.

Over the years his asthma has gotten worse. It is to the point now that even the dogs will aggravate his symptoms under the right conditions. My mother has to give him a warning that she’s going to be vacuuming. He then has to leave the house for hours on end until the dust settles down again.

How often do you replace the filter?

If you or someone in your family has symptoms similar to this, or perhaps just suffer from a more mild form of allergies, there are options that you can do to better outfit your home so that your loved ones are as comfortable as they can be. I’m not going to get into every possible option in this article but instead focus on one of the easiest, and some would argue most impactful, change you can make to your home.

Most of you know that you need to change your air conditioner/furnace’s filter every two months or so. But, what a lot of you may not know is that the quality of the replacement filter you are purchasing can make a huge difference. In the past I used to run to the local hardware store and purchase the cheapest filter there in the size I needed. While this filter got the job done I was getting what I paid for, which was poor quality.

MERV Rating

These filters that I was purchasing were mostly rated as a MERV one, two, three, or four. These are the lowest of the low when it comes to furnace filter ratings. 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.

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.

Also, in a continuing effort to help my father out we use the high quality filters and we also use air purifiers in our living room and his bedroom. Typically the combination of the AC/Furnace filters and the air purifiers keeps him in pretty good spirits.