Re: RabbitAir Bypassing?

A Reader writes:

Hi Ed,

Your site is excellent and I just want to thank you up front for your hard work.

About a month ago I purchased 2 RabbitAir units the bioGS 421a and the 528a.

I made the decision based on all the positive feedback I read from at least 10 or so websites.

Then I read your review and much of your site and went ahead and bought the two rabbits from vitacost.com which sold each model $30 dollars cheaper than any other vendor on the internet and they also offered free shipping.

About the rabbits since I couldn't find any information about the machines particle output or by-passing, I tested them by running both for about 30 days 24/7, 90% of the time on high or turbo.

I then removed the 3 filters and ran my finger around and across the fan housing.

As I did this I could feel a very small particulate buildup which also appeared on my finger as a very fine powder, not much but enough to realize that there was bypassing taking place.

I cleaned both machines thoroughly then replaced the filters back in the proper order. First the carbon filter then I sealed it in with 3/4 inch tape around the perimeter to cover the gaps,

I then put in the hepa filter and lastly the nano pre-filter also using 3/4 inch tape to seal the filter in place.

I will run them for another 30 continuous days and recheck the area behind the filters.

My question to you is this bypassing normal for an air purifier in this price range and does this change your mind about the rating that you gave it.

I think you should also know that I called RabbitAir and talked with a consultant, and when I told him of my discovery he did not try to refute my finding that the unit wasn't sealed.

He politely reminded me that they have never made a claim in their ads that it was, he went on to explain that in order reach the goals of acceptable CADR and noise levels the engineers had to design the units in that fashion, he also apologized to me that I was troubled by my findings and he also told me that I could keep the units up to 1 year and if I still was not satisfied I could return them and get a full refund.

I suggested to him that rabbit make a gasket for about $10 and sell them to customers that didn't want any bypassing taking place.

He didn't really have a response to that idea.

I told him that I was going to try to design a gasket and if it solved the problem I would keep the units.

My next question is would you recommend a certain type of material that I should use or is it alright to just use the tape.

I also made a tremendous mistake about buying the right size units, my condo is two floors and the downstairs is about 600 square feet give or take a few feet, and upstairs is smaller with two bedrooms and 2 bathrooms they are average size.

What do you think about the Airgle 750 for the down stairs area, I was concerned a little that it doesn't seem to generate negative ions, would this be a deal breaker for you?

It also seemed the most powerful unit to deliver 5/6 air exchanges per hr. in that price range and replacement filters seemed reasonable, am I on the right track?

I know that I will need another unit to really keep the air in my place safer.

The IQ is out of my price range especially in the replacement filter area.

Another consideration is that American Express lists the 750 in their rewards program with a 10% discount and I have more than enough points to cover the entire cost.

Any feedback would be really appreciated.

Regards,

Ed's Reply

Hey Reader;

You have discovered a couple things.

First: Most air purifiers are designed to bypass a percentage of the air inhaled. It is the percentage actually filtered we call "single pass efficiency."

(Note that we are talking in non-scientific terms here - single pass efficiency technically requires a particle size specification to be meaningful, we are omitting that).

Many cheap air cleaners, and some very popular and overpriced machines, have efficiencies below 50%. Mid-priced purifiers, like the RabbitAirs, might score in the eighties.

See Comparison Chart at AirPurifiersAmerica.com

This chart is an illustration of relative performance only. Note that Alen is the house brand at air-purifiers-america, they have reason to promote it.

Many air cleaners have channels that divert air to sensors, allowing a small amount of air to evade filters.

By building tightly sealed machines, the IQairs for example, the builder sacrifices price, noise, and CADR marketing in return for high efficiency.

IQAir continues to do this, despite poor ratings from clueless Consumer Reports, targeting quality and health conscious premium class consumers.

But because of this, their $1000 HealthPro Plus has about the same throughput as a $200 250 CADR Honeywell.

If you want zero bypassing, you'll have to go premium class.

I have recently purchased a RabbitAir BIOGS 421A, and am impressed with the overall quality. But, as you have demonstrated, it is not perfectly sealed. The Mitsubishi design, in a departure from industry practice, places the carbon box filter last.

This, and the lack of a filter cassette tray, means any tape or gasket stuffing must seal the HEPA directly.

I'd start with some scotch tape rather than gasket building. I don't think the Rabbit's HEPA edge gaps are wide enough for polyurethane foam stuffing.

Sealing the prefilter screen will lengthen HEPA life, but you must seal the HEPA itself to prevent the key bypassing danger - ultrafines.

Also, there is no need to seal the carbon filter case, carbon filters let lots of air through gaps in the carbon granules.

Efficiency of chemical adsorbtion is a completely different issue, focused primarily on activated carbon quality and additional adsorbent choice.

Another possibility is that the filters are not held against the back of the case tightly enough. Other air purifiers in this group use the front cover to apply pressure. The 421A seems to have a bit less.

It will take me a couple months to evaluate this new machine (along with four other new purifier tests). Sealing experiments will take even longer.

Remember that total seals require higher quality motors - we must avoid over-sealing.

I have burned up a brand new $100 Hunter Permalife 30748, by installing extra prefilter material, in just a few hours operation.

Note that the "Permalife" filter is not-HEPA, designed to capture 2 micron and up particulate - built in bypassing of critical fine particles.

Extra sealing should reduce airflow only slightly, if the purifier goes "quiet," you have over-sealed.

Second: RabbitAir has exceptional customer service. Their honesty concerning this matter is unusual in this smoke-and-mirrors industry.

Note that RabbitAir is an importer. They do not design and build the air cleaners they sell. The company works closely with manufacturers, namely Mitsubishi and Coway, but cannot directly offer design modifications like gasket kits.

I consider Rabbitair the best importer/rebrander among many in the US.

Many other vendors would not respond to any criticism. Some never answer the phone, others screen email, ignoring any claims or complaints.

I continue to rate the RabbitAirs slightly higher due to the company's excellent communication skills.

For instance, there was an issue with fragility of carbon replacement filters, some were damaged in shipping.

Quickly responding to user feedback, RabbitAir corrected this issue with a nice, though not easily user refillable, durable plastic case for the carbon.

This kind of response will probably not be the case with the Airgles.

While Airgle 750 is a very strong machine, sales are below expectations, and stateside customer service is soft.

Note that the 750 has four sets of filters to replace.

The lack of a negative ionizer, often an inferior add-on, is not a deal breaker.

I prefer the Blueair 603 for large area particle clearance, but high filter costs may deter you from choosing it.

Airgle 750 is the first mainland China product reviewed positively here, primarily for its high power.

I consider it a risk in today's market consolidation. With your concern about filter costs, how would you feel if no replacement filters were available in two years?

But hey, I am always looking for buyers to test a product and report their results. You could be the first.....

My oldest IQAir has run almost five years with the original HEPA, and still shows zero exhaust particulate with a laser particle counter.

I replaced the prefilter for $60 after four years, and removed the V5 carbon cell, which had picked up some odor sitting near an open window in not-so-pristine uptown Houston.

A new V5 cell would be about $90.

I consider this very reasonable maintenance.

The secret to long HEPA life is not to use the main filter to collect large particles. Blueair's weakness is the lack of separate washable prefiltering - their progressive filters are effective, but must be replaced when clogged.

Blueair's engineering is a different approach to the throughput/bypassing quandary every builder must face.

HEPA vacuum cleaners, used regularly, will reduce visible and coarse dust, making HEPAs in air cleaners last longer.

I hate vacuuming, so I use cheapie air cleaners, modified as coarse dust catchers, in my residences.

See remarks on improvised coarse dust prefilters for IQAirs in;

The Prefilter Experiments.

Best wishes,

Ed