Can I Get A Better Filter For My Mini Split?

You will find here that I’m not going to say yes or no, but here’s what you should know. Increasing the efficiency of the filter for your mini split can reduce your units efficiency, possibly damage the unit, and can even result in your warranty becoming void.

Now if that didn’t cause you to read more and dig is a little deeper then you don’t scare easy. But what I said about increasing filter efficiency is true with any HVAC system that requires a filter. The higher the efficiency of the filter, the more restrictive the filter will be to air flow.

Heat pumps, air conditioners, and furnaces that move air need a specific amount of air flow. You can find that amount stamped right on your equipment’s label. It’s the part that gives you the static pressure. I have an article that talks all about static pressure and you can read it here now (or come back later).

When most home owners become concerned for cleaner air they jump to the internet (what did I say, you’re here) and start searching for a high efficiency filter or best furnace filter. Without too much hesitation they reach for the highest MERV ratings or even a HEPA filter.

Some definitions are in order. MERV stands for Minimum Efficiency Reporting Value. A relatively new system that measures all filters on an equal basis instead of each filter manufacturer measuring their own filter and coming out on an unequal basis.

HEPA stands for High Efficiency Particulate Air filter. HEPA filters are used mostly in medical and industrial applications like a cleanroom. Those applications need to move a lot of air to be able to use such filters. Your furnace may not have the horsepower or required air flow in it’s blower to stay within the required static pressure when using a HEPA filter. It needs to be measured with a manometer to know.

The Best MERV Rating for Residential HVAC System Use
According to the ASHRAE, the best rating for residential HVAC systems is MERV 13. But before you upgrade your filter, make sure your specific system can accommodate that rating. A higher MERV rating often means lower airflow, which can cause the system to work harder—use more energy—to do its job. If your home HVAC system is not capable of handling MERV 13, opt for a filter with the next highest rating possible.

Bob Vila

I remember the first blower motor I changed out in a mini split. It was a factory default and I never want to change out another mini split indoor blower motor. It took forever. They are very small in dimension. And compressed into a very tight area. Theirs not much hope for such a tiny motor to overcome the static created by a more efficient filter.

The engineers that design these units, no matter what brand, have considered the the air flow and the compactness of the indoor units down to the most infinitesimal degree in order to keep mini splits small. They don’t call them mini’s because they’re big and powerful.

Can I Improve My Mini Split Filter Or Make It Better?

Their are a host of products that claim to help catch more particles. Most come in the form of a spray. Amazon has a huge selection of items but only a few that are specific for your air filter. When searching for “furnace air filter spray” be careful to not select the automotive sprays like K&N. It’s a little deceptive and the wrong application.

These products make the filter a little sticky and help catch finer particles that could actually slip through a filter and collect on the indoor coil and blower assembly. Believe it or not, in the past I have used WD40 on some of my customers filters and even my own filters. I would get permission first of course, because WD40 is more of a solvent and can have an offensive odor. The odor soon dissipates and whether it really helped or not, well that’s debatable.

There is a little oil involved in WD40, after all the WD stands for “water displacement“. Did you know that? As long as I’ve used that stuff I didn’t know or even think about what the WD stood for. So a little WD40 lubricant can help make your mini split filter tacky and collect some of those smaller particles that you wanted to catch using a high efficiency filter if you can get past the idea of it and the initial odor.

Best to be cautious though. Like I said I used WD40 in the past. It was before we saw much in the way of mini splits. These mini split filters are very thin and I’m not sure of the material they are made of and what the reaction would be to a solvent like product. Try to use something with an intended purpose.

Other products that are made specifically for improving your filters efficiency are probably more palatable. For example Web Filter Charger that claims to have an adhesive to capture dust and particles and has a fresh citrus scent. Be sure to read carefully when wondering around that Amazon site as well as others. The various products can be misleading, not intentionally, just a little on the confusing side.

You might also want to study up on a few of those filter cleaners that help keep your filter fresh and new looking.

Another thing that may help depending on your local humidity or climate. Two small attachments that clip right onto the surface of a mini split filter and come with most of the new mini splits that I’ve sold anyway.

When I unboxed my first mini split and opened the paperwork pouch with these weird looking little filter like things inside, I thought what kind of hocus pocus is this and what good could they possible do as I said they simply attach onto the surface of the filter.


I have no actual proof that these filter attachments work other than what the different manufacturers say. They make a lot of talk about clean air and global warming and as soon as that begins I get a little wrenched up inside because of the confusion and the politics. But nonetheless these little addons could be and answer to your clean air.

Fujitsu calls one of them a Polyphenol Catechin air cleaning filter. I have a lot more to learn about these little gadgets and perhaps when I do, if I do, I’ll write some more about them. You might know more about them than I do or perhaps you are a better researcher.

Give it a search by entering your particular manufacturer and add filter to the search, like “Mitsubishi air filter” or Fujitsu or Daikin. Those are the main brands that I have used and they all have these little added attachments for filters that could help you.

From Daikin Operation Manual

To get a little better idea of what I’m talking about you should search Mitsubishi min split filters. Look for PLASMA DEODRIZING FILTER, and an ANTI-ALLERGY ENZYME FILTER, and a PLASMA ANTI-ALLERGY ENZYME FILTER, and a CATECHIN AIR FILTER, and a couple more. It looks like these are mostly disposable and you need to replace them from time to time. Not washable in other words.

These are the hocus pocus filters that I mentioned. They may actually help you. I honestly don’t know. Like so many things out there the proof is in the pudding. Give them a try if you feel so inclined, what could it hurt other than a few dollars.

Chad Peterson

Chad Peterson is a veteran of the HVAC industry since 1977. "I like to explain heating and air conditioning problems in a way the average home owner can understand. "

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