What’s CADR and how is it different from airflow?

ओह! यह पोस्ट हिन्दी में उपलब्ध नही हैं।अंग्रेजी संस्करण के हेतु यहाँ क्लिक करे l

Thomas Talhelm

Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.

4 thoughts on “What’s CADR and how is it different from airflow?

  1. I just moved to China and I’m trying to sort out what I need for my apartment (61.3 sq m, 2 bedroom + 1 hall) assuming I use one of your filters at low or medium for reduced noise. But I need some information I can’t find on your site.

    1. What is the CADR for your products (especially the Blast and mini Blast) at low and medium speed? I’m assuming the amount listed on your website is for high speed.

    2. What is the calculation to determine one’s CADR needs? I found the following on a post by Dr. Saint from myhealthwellbeing.com posts: sq meters X ceiling height X 5 (because air purifying requires 5 air changes/hr) = CADR required. But this seems off because it means the Blast at high (with a CADR of 890) would only work for a room that is 71.2 sq meters assuming normal ceiling height of 2.5 m (71.2 X 2.5 X 5 = 890) while your site says it is good for 130 sq m. Even if the air changes/hr was 4, the calculation is still off (it would mean a room size of 89 sq m). So where is my mistake?

    3. Can a single air filter be used for an entire apartment even if the bedroom doors are usually closed? (I’m assuming the total area is within the CADR of the filter).

    Ps: would be great if you posted this calculation on your site in the “shop” section and eventually had a simple CADR requirement calculator on the site or an excel one that could be downloaded to determine one’s needs and which of your products to get.

    1. Hi Ak, great questions. Looks like you’re being smart about working out your clean air needs! To answer your questions:

      1. I’ve updated the Blast and Blast Mini pages to include the CADR on the different speeds. Thanks for pointing this out!
      2. There are many different methods for calculating area based on CADR, all based on different assumptions and for different countries. For calculating the area, we use the China Government Standard, along with our own real life testing. The China standard says to take the CADR (in cbm/hr) and multiply by 0.07 – 0.12. So a CADR for the Blast of 890cbm/hr would give a room area between 62sqm – 109sqm. Based on our own tests in Beijing we found these to be pretty conservative, so we use a slightly looser rule which is why we claim the Blast to be good for 130sqm. Bottom line: if you want to be conservative take the CADR and multiply by 0.12 to get roomsize.
      3. From our tests, we’ve found that closing a door means not enough clean air does travels between rooms. So our advice is to have a purifier in each room. Of course, it all comes down to how a) leaky your windows are in the room without a purifier and b) how tight the seal is round the door. If you were to leave your door ajar then you should be fine.

      And regarding your P.S. point – that’s a great idea and something we’ve wanted to do for a while. We’ll work on getting something like this up!

  2. I love your site and all the data you’ve collected. Two things I’m curious about:
    1) How much does the flow rate change between with the filter and without?
    2) How much does the noise level change between with the filter and without?

    I’m asking because I’m curious about using a different fan with a known flow rate but a lower known noise level. If your data is correct, you’ve beaten the competition in CADR, price. Do you think it’s possible to maintain this performance while reducing the noise to a whisper? (I have faith)

    1. Hey Vincent, thanks for the kind words. Two good questions!

      1) We’ve not done tests on the airflow without a HEPA, but if we look at the numbers for the Cannon, which claims a max airflow of around 700cbm/hr, we can see that the airflow is reduced at least
      2) This is a much more difficult question to answer, since sound is much more a subjective thing. In terms of actual sound levels (measured in dB(A)) there is little difference between the fan with and without a HEPA, but in terms of what kind of sound you get (‘windy’ sound with just a fan or a kind of ‘whooshing sound’ with a HEPA – sorry if that doesn’t make much sense!) it is very different. Generally, with a HEPA it sounds more pleasing/calming.

      In terms of making a super quiet yet super effective purifier, we think we did a pretty good job with the Blast and Blast Mini! Ultimately to reduce noise you need a big HEPA and a big fan. This means the air can move more slowly through the whole machine, reduce the noise it makes as it passes through the HEPA filter. Check the Blasts out if you haven’t already!

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