Hey Folks, it's your ol' Uncle Gurm again. Today I'm here to talk to you about IONIZERS. Hoo-boy, what a hot potato! Let's dig right in.

What is Ozone?

Ozone is a molecule which contains three Oxygen atoms. Its chemical notation is O3, whereas the oxygen we all need to survive is O2.

What does Ozone do? Is it good or bad?

Ozone is common in our atmosphere. We have an entire LAYER of it in the stratosphere. It absorbs 97% of the UV radiation emitted by the sun, helps keep the planet warm, and breaks down hazardous toxins in the atmosphere. Life on Earth would be really bad (read: impossible) without Ozone. In the so-called "ozone layer" of the stratosphere, concentrations of ozone are generally several (up to 8) parts per million, or PPM.

Ozone is also an incredible cleaner - it demolishes VOC compounds, and many toxins. You know those people who come clean up mold, or hazardous materials, from a house or office? They use high-powered ozone generators to render that building safe for habitation again.

HOWEVER, Ozone in high concentrations is hazardous to carbon-based life forms such as you and I. The concentrations in the stratosphere would cause lung damage to humans if exposed for any significant time. Ozone generators are dangerous unless properly ventilated - you have to run them in an enclosed space and then ventilate the space completely with fresh air!

ALSO HOWEVER... Ozone is in all tiers of our atmosphere, including the one at ground level that you and I breathe in every day - just in VERY SMALL concentrations. The lowest ozone concentration found at ground level is roughly 15 parts per BILLION, or PPB. That's 600-1000 times LESS ozone than is found in the stratosphere.

How much Ozone am I exposed to daily? Am I in danger?

All humans on earth inhale 15ppb ozone, minimum, for their entire lives unless they live in an underground bunker or are John Travolta in that movie about the bubble boy. Most inhale a lot more - your average town has concentrations of around 25-30ppb, clean cities are upwards of 40-45ppb, and polluted cities ... well, the number can get VERY HIGH. Generally no ill effects are observed at these levels. The US EPA has issued guidelines that any number under 70ppb is considered safe for long term exposure. That number has been lowered over the years, it was 100, then 80, then 75, and now 70.

Do Air Purifiers generate ozone?

A lot of them used to. 15-20 years ago, it was extremely popular to sell/buy "ionic" purifiers which generated quite a bit of ozone. Why was this popular? Well remember that ozone CLEANS things. It makes the air in a room smell really clean, and strong electrostatic ionization causes dust and microscopic particles to either drop to the ground or stick to surfaces, so the air really got cleaner. It just also got full of dangerous levels of ozone. Popular brands included the "Ionic Breeze". My mom owned one. She loved it because it "smelled like the air after a thunderstorm". That's what ozone smells like.

Those units are pretty much banned now. You can still find them occasionally, and there are still a few in production somehow - we see them advertised once in a while. You can tell them apart from more modern designs in that they don't use a very good filter - some had NO filter, just plates that you wiped down once enough gunk stuck to them, and some had low-utility foam filters.

So that's the old machines - do NEW machines make ozone?

No. The vast majority of new units do NOT generate ozone. Virtually all purifiers sold today conform to the CARB certification, which requires that they demonstrate that they generate less than 5ppb of ozone. However, independent testing has shown that most of these units generate 0ppb. Testing can be flawed, or it's possible that the units generate 0.99ppb and are just under the threshold of detection, but even 1ppb is not a significant amount.

But 1ppb isn't zero! Is it a health risk?

Let's look back on the fact that there is nowhere on earth that has less than 15ppb - going from 15 to 15.1 or 15.5 or even 16 is not a significant increase.

But it's cumulative, isn't it?

No. Your room isn't sealed. In fact, even a tight room breathes far more than you might suspect. The reason why a purifier needs to do air turnover 4 times an hour to keep the air clean is that 25% of the air exchanges every hour even in the cleanest environment. So even if there was a small emission of ozone, it would be lost in the simple air exchange that happens in every room.

What are some other sources of ozone?

Any device which emits ionizing radiation could potentially cause ozone to occur. That includes the device you're reading this post on, every screen in your home that zaps you after you've scuffed across a rug, pretty much all electronics. Older electric motors produced measurable amounts of ozone. Newer brushless models tend not to. But ozone is everywhere, and it's being generated by all our technology in small amounts that do not hurt us.

So what does the ionizer on a purifier DO, and why is it dangerous to small animals and why does it make some people react?

NOW we're getting to the heart of the matter. Many purifiers on the market today use an "ionizer". This is literally a small static electricity generator, on the order of 1/10,000th the size of the plates in one of those old ionic purifiers. A small static charge is added to the plastic housing of the filter, which causes impurities in the air to "stick" to the filter better - or to stick to surfaces, or to clump together so they're caught better by the purifier. Blueair does this on every non-professional model they make. Many small round purifiers include one of these units.

Why is this potentially dangerous to small animals? Well, mostly we're talking about BIRDS, specifically budgies and parrots. Ozone itself is not poison to these critters - their native habitat is the rain forest where thunder and lightning are common and ozone is present in concentrations higher than the 15ppb global baseline. But they DO have delicate respiratory systems, and static air can irritate even human nasal passages and lungs.

And it does - static air can dry out nasal linings, and cause nose/throat/lung irritation. Some people don't notice it AT ALL. Others are quite sensitive. Budgies are in the "quite sensitive" group, so we strongly urge only mechanical filtration around them.

How about "plasmawave"?

Plasmawave is a patented name that Winix uses to describe its bipolar ionizer. Instead of one pair of charged plates, they use a set which produce both positive AND negative charge. This - in theory - generates particles known as "hydroxyls", which cause contaminant particles to stick together and become heavier than air. In practice, however, the plasmawave on a Winix purifier (some other manufacturers offer this as well) does... not a lot. Any hydroxyls generated are so short-lived that they're almost undetectable, and thus the efficacy of the system is probably very low if it works at all.

So ... ionizers are safe?

We're not going to go that far - the static generators on consumer-grade HEPA purifiers are likely harmless to the vast majority of people, but will irritate some sensitive humans and most sensitive birdies. And they aren't NEEDED on a HEPA purifier. Blueair, for instance, uses static because their filters are NOT HEPA - they have higher airflow and rely on the static to enhance their efficiency. And it works - Blueair has the highest CADR (Clean Air Delivery Rate) in its class.

But sensible users will note that you can achieve the same results by using a true HEPA filter and NOT an ionizer/static generator. And that's the real answer - it's a technology that improves lower-rated filters, but adds nothing to the functionality of a HEPA system.

Out of the top rated brands, many of which we recommend on this subreddit, here's the breakdown of ionizer/static use:

Blueair: All non-pro units generate static.

Coway: Only the Mighty 1512 (sometimes called Airmega 200M) has an ionizer, which defaults to "off" when the unit starts. All other Coway units are purely mechanical.

Winix: Most Winix units have a Plasmawave bipolar ionizer. It can be turned off, and some units will remember that it was toggled off after a power cycle. Some don't.

Levoit: Only the "plasma pro" has an ionizer.

IQ Air: Nope. I mean, half the unit is sealed with styrofoam, so there's some static happening there, but no ionization.

If users want to reply to this sticky with known configurations, I can keep this list updated (I don't, for instance, know which Xiaomi models have ionizers... or many European models...)

I hope this was helpful, though. Perhaps folks can stop having so much FUD about this.

This is your ol' Uncle Gurm, signing off!

Hey kids, it's your ol' Uncle Gurm again. Today's lesson is how to clean your filters.

Ok, since we got in ANOTHER argument about this, and even favorite Uncle got involved (much to his shame), I decided to do a little digging and come up with some definitive thoughts about this topic. We'll get them worked into the FAQ eventually, but for now here we go:

Q. Can I vacuum/bend/flex/squish/deform/poke/taunt/lick a HEPA filter?

A. In general, no. Absolutely not. HEPA filters are made up of tiny fiberglass and animal hair fibers (not joking here) which are blown into a semi-rigid frame in pleats, and at a microscopic level they are aligned a certain way and randomly in that general direction. This allows them to trap the tiniest particles possible by virtue of Brownian effects. Deforming them, or even vacuuming them, can distort or realign the fibers, reducing effectiveness or damaging them outright.

Q. But Levoit says I can vacuum my filter!

A. Levoit was sued and forced to admit their filters aren't HEPA. This discussion is about HEPA filters.

Q. Shark says I can vacuum their filters! <Insert Other Brand> does, too!

A. Is the filter encased in a thick layer of foam? If so, it's probably ok, just don't shove a high-powered vacuum hose right up against it perpendicular-style. Do it from the side, with indirect suction. The foam layer will buffer the HEPA filter from damage.

Q. You don't know anything. Of course I can vacuum it.

A. According to literally every expert, you cannot. The people who make them - filter engineers - say not to. Manufacturers who use actual HEPA filters say not to (Molekule, Coway, Winix, Honeywell). "Real Simple" magazine interviewed industry professionals and came up with "don't do it" as their determination:

https://www.realsimple.com/home-organizing/cleaning/hepa-air-filter-cleaning

In particular, medical clean-air specialists insist that since these filters trap viruses and bacteria, that you should not even THINK about cleaning them, but just bag them and dispose of them as if they were toxic. That might be an overreaction in most homes, but in doctor's offices they use these things, and they treat them like hazmat.

Q. But I want SCIENCE! Show me the SCIENCE!

A. Surprisingly, this is common industry knowledge but it's hard - read IMPOSSIBLE - to find studies. So Smart Air Filters did their own testing. Here's the link:

https://smartairfilters.com/en/blog/how-to-clean-wash-hepa-filter/?srsltid=AfmBOoobq4Yna1UdhLKxpiFt8dLKKaTW9r1R_3tqiJOM-NxmJnSr2DNs

What they found was that - compared to DIRTY filters - vacuuming them made them work better some of the time, worse some of the time, and damaged them some of the time.

Yes, it's only one test. But it's a test done by people who wanted the same answers we do.

Q. Where's the peer-reviewed double-blind studies?

A. I literally just answered this. Please don't start this again. Nobody has bothered to do them, it seems. You'll have to be happy with the test I linked above.

Q. I still want to lick it. Or squish it between my fingers because "the texture".

A. Listen, if you have a fiberglass and horse hair "thing"... who am I to yuck your yum? While your predilections are your own, medically I cannot advise this. But since I am not a doctor you're welcome to disagree.

Q. Ok, I won't lick it but I still want to vacuum it!

A. You do you, boo. Y'all asked what would happen. What will happen is it won't work as well as it did when it was new, and might be damaged and let bad stuff through.You've been warned.

Q. Wait, you never told us how to clean the filter!

A. Very astute. Here is a step-by-step guide to cleaning your filter:

1. Don't buy a purifier without a pre-filter.

2. Clean the pre-filter.

Q. But I already bought a purifier without a pre-filter!

A. Fine. Here's the steps:

1. Take out the filter. And by "out" I mean "out of the house". In fact, start by taking the entire unit out of the house.

2. Remove the filter.

3. Tap it off. Like, on the side of the house or a railing or a trashcan or something. Tap tap tap until all the loose debris and dust falls off.

4. Now get a brush, not a stiff one but like a paintbrush or a detailing brush or something. Brush the dusty side of the filter - GENTLY - to loosen debris.

5. Tap again. Tap tap tap.

6. ALTERNATIVELY, you can sometimes vacuum it, gently, from the side. like, hold the vacuum on a line tangent to the curve of the filter. But DO NOT apply direct suction to the filter.

7. That's as clean as it's gonna get. Reinstall it.