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Joey Fox, P. Eng, M.A.Sc Profile picture
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Jan 26 • 8 tweets • 4 min read
COMPARING HEPA FILTERS AND THE #corsirosenthalbox 🧵

Both HEPA filters and CR Boxes do the same thing - they filter the air. Which one is better? I'll compare the CR Box to 2 HEPA filters: Levoit LV-H133 & Austin HM400.

Criteria are: CADR, noise, cost, structure.

1/7
CLEAN AIR DELIVERY RATE (CADR Dust CFM)
CR Box: 290-600
LV-H134: 274
HM400: 250

NOISE (55 dB is about the threshold for tolerable in a classroom.)

CR Box: 49-54 dB
LV-H133; 54 dB
HM400: 62 dB

COST (CAD before tax)
CR Box: $90-120
Levoit LV-H133: $329
Austin HM400: $850

2/7
STRUCTURE

CR Box: 10 lbs
Levoit LV-H133: 21 lbs
Austin: 47 lbs

CR Box is bulky and easy to break. It can be easily damaged with a pencil. But the large shape is what allows it to filter so much air. The filters have a lot of surface area and the fan is 20".

3/7
Both Levoit and Austin are about 14.5". They are smaller and sturdier. The Austin is extremely durable.

There might be some industrial or medical applications where the Austin is appropriate, but 62 dB is loud for a classroom and it is the most expensive by far.

4/7
I picked the Austin HM400 because it is found in many schools and the Ontario gov't purchased 30k of them.

I picked the Levoit LV-H133 because it is one of the best ones to use for a classroom.

5/7
Unsurprisingly, the CR box has the best CADR and the lowest price. It's a great option.

Many school boards would be hesitant to put in a DIY filter. I've seen people hesitant to use HEPA filters and only want CR boxes. HEPA filters are just as good. Just filter the air!

6/7
REFERENCES

There's a range of values for CR Boxes. It depends on the fan and setup.



austinair.ca/products/healt…
cdn.shopify.com/s/files/1/1002…
levoit.com/products/lv-h1…



7/7
ADDENDUM - FILTER REPLACEMENTS

Levoit LV-H133: $86 every 6-8 months
Austin HM400: $370 every 5 years
CR Box: $15-90 every 6 months. When the pandemic ends, you can reduce it to 1 or 2 filters instead of 4. Slight reduction in CADR, but much cheaper filter changes.

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More from @joeyfox85

Joey Fox, P. Eng, M.A.Sc Profile picture
Jan 26
PUTTING MERV-13 FILTERS IN AIR HANDLING UNITS 🧵

Many schools have replaced the standard MERV-7 or 8 with MERV-13 filters in the ventilation systems. It's a simple method to filter viruses from recirculated air, but doesn't always work. Here are some issues to consider:

1/6
MERV-13 filters are efficient at filtering out aerosols that contain viruses unlike MERV-8, but they also create a greater pressure drop and restrict flow. This is why ASHRAE recommends units to be rebalanced when filters are upgraded:

ashrae.org/technical-reso…

2/6
What happens if this isn't done? Air handling units could have 2 purposes: ventilation only or ventilation + temperature control.

If it's ventilation only, you will be providing less fresh air to the space. There will still probably be a net benefit, but this isn't ideal.

3/6
Read 6 tweets
Joey Fox, P. Eng, M.A.Sc Profile picture
Jan 24
ORIGIN OF THE HEPA FILTER LIES

I've been spending a lot of time recently debunking lies about HEPA filters. They have been propagated by school boards and politicians as an excuse to not put them in classrooms. Who started them?

1/8
In August 2020, I asked my kid's school to put HEPA filters in the classrooms. I was overruled by a public health official who raised these misguided concerns. For the record, this is no longer the case and the school is making great efforts to make the place safer.

2/8
It's bad actors in IPAC, infectious disease physicians and public health officials who have been controlling the response to this pandemic. They still deny that #COVIDisAirborne . The politicians, media and school boards listen to them.

3/8
Read 7 tweets
Joey Fox, P. Eng, M.A.Sc Profile picture
Jan 23
IMPROVING SCHOOL VENTILATION MOVING FORWARD

In my mind, there are 3 different issues at play:
1. New construction/Renovation - I'm not concerned about this. There will be a lot more research on air quality and health and there is now public awareness about its importance.

1/9
I have confidence that ASHRAE will update the guidelines based on our new societal values and we can make new designs better moving forward.

2. Under-ventilated buildings - many buildings built in the 50s-80s don't have proper mechanical ventilation.

2/9
How do we deal with this? Do we mandate filtration or UVGI? Do we have to demolish and rebuild a significant percentage of our buildings? Do we continue on as in the past? Heat recovery ventilators can be used sometimes, but not always.

3/9
Read 9 tweets
Joey Fox, P. Eng, M.A.Sc Profile picture
Jan 21
HEPA FILTER MYTH vs. FACT

When the novel coronavirus burst onto the scene, it quickly realized that the mighty HEPA filter was one of its greatest foes.
It began an aggressive anti-HEPA filter lobbying campaign with politicians, public health officials and school boards.

1/9
The goal was to spread lies about HEPA filters to ensure it could infect as many kids as possible. These gullible individuals have been doing PR for the virus and the lies need to be put to rest.

2/9
Myth: HEPA filters blow the virus around
Fact: They remove the virus from the air

3/9
Read 9 tweets
Joey Fox, P. Eng, M.A.Sc Profile picture
Jan 19
THEY BLOW THE VIRUS AROUND

This is one of the most prevalent lies against HEPA filters. It’s been used by school boards and politicians as an excuse to not put HEPA filters into schools. This myth needs a thorough debunking.

1/9
AEROSOL SPREAD IN A CLASSROOM

The air in a classroom is well mixed. Anyone who is concerned about blowing the virus around needs to know that it's already been blown around. Here's a diagram of what classroom airflow looks like:



2/9
Here's a document from ASHRAE discussing the well-mixed assumption for classrooms.

"...the well mixed assumption in the Wells-Riley model may hold better for these [smaller] particle sizes."

ashrae.org/file%20library…

3/9
Read 9 tweets
Joey Fox, P. Eng, M.A.Sc Profile picture
Jan 17
THE MINI #corsirosenthalbox

Here it is:

1/6
Fan from here:
(the one displayed on the wayfair website was not the one shipped. It's seen on the amazon website.)

2/6
wayfair.ca/home-improveme…

amazon.com/Comfort-Zone-P…

H/T @Flying_Donny
Filters from here:

3/6
amazon.ca/FilterBuy-10x1…
Read 6 tweets

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