Thread by @joeyfox85

How I'm rating the HEPA filters purchased by Canadian schools 🧵

I will tweet a thread soon comparing some HEPA filters purchased by Canadian schools. Before, I want to explain my rating system here.

1/8

Getting the info about the HEPA filters was very difficult - it isn't available. The proper info provided for each one should be the CADR (clean air delivery rate) and noise at each speed, but you can't find that, so I had to estimate based on the available information.

2/8

Many companies provide misleading info. For example, they state the CFM of the fan without the filter instead of the CADR. They state the noise at >6 ft away rather than the standard of 1 m. You have to sort through the nonsense to find the necessary info.

3/8

I then had to determine a rating system. You are looking for cost, noise, CADR and no ionizers. If something is too noisy in a classroom, it just gets turned down, so I decided to use my estimated CADR when on a speed with the noise under 55 db - usually medium speed.

4/8

This estimate isn't super accurate, but I think it is in the ballpark of the correct value. 2 categories CADR @ < 55db and $/CADR @<55db:

CADR @ <55db
CADR Points
250+ 5
200-250 4
150-200 3
100-150 2
50-100 1

5/8

$/CADR Points
<2 5
2-4 4
4-6 3
6-8 2
8-10 1

Electronic air cleaning = -2 points

In the end, they get a mark out of 10.

6/8

For reference, the one I recommended here is the Levoit LV-H133. 275 CADR @<55db and costs $1/CADR. Easy 10/10.

If you went to a hardware store and played ini mini miny moe, you would probably pick a better HEPA filter than in most classrooms.

https://twitter.com/joeyfox85/status/1483462543314239490?s=20&t=bv5_sLg0zDNV2amMo4wlsQ

7/8

The point is, I created a very generous scale because the HEPA filters in schools have low CADR and cost a fortune. If I hadn't done that, they would all fail. This scale allows you to compare between school boards. Stay tuned. The ratings will be out soon.

8/8