Why isn't my purifier achieving its rated room size?

It's 70 inside and rising. As my family move into a small room I wonder why isn't my purifier working?


Purifiers come with a recommend room size. However I have found at times my purchased purifier cannot do its max size of 79m2. I noticed it really struggled as dense smoke rolled in and outside was over 100 PM2.5.

I have come to learn that house leakage is quite high in Australia, on average around every 77 minutes all the air in your house is replaced with air from outside. As such the size a purifier can do is highly based on outside levels.

Using a spreadsheet I have simulated the maximum room size based on outdoor PM2.5 readings. I have assumed the house is leaking at the average found by CSIRO.

The aim is to have indoor readings under 10 PM2.5.

Max Room Size m2 to have under 10 PM2.5
Outside Level	DIY @ 531m3/hr	Phillips 2000 @ 424m3/hr	DIY Big Boy @ 1300m3/hr
25	72.10	86.00	157.00
50	28.30	34.30	61.00
75	17.4	21.1	37.9
100	12.6	15.2	27
125	9.8	11.9	21.25
150	8.1	9.7	17.5
175	6.8	8.3	15
200	8.2	7.2	12.9

FYI DIY Big Boy is not built yet, but based on the 60cm x 60cm MERV 16 filter with a face velocity of 1m/s.

The results show that my Phillips air purifier can only do the rated size when outside levels are under 27 PM2.5. Given the extremely high levels recently now I understand why it wasn't working.