Air purifiers are often rated and marketed on the basis of their airflow – how much air passes
through the purifier, usually measured in cubic feet per minute. A similar rating is the ‘CADR’ or
Clean Air Delivery Rate, which combines the air flow with the efficiency of the particulate filter.
So purifiers with high airflow and CADR are seen as good. However, at Plain Air we know you need
to look in more detail.
The more air passing through a filter, the more opportunity there is for particulates to be trapped,
and the faster your air will be cleaned, surely?
However, speeding up airflow does two things. Firstly, it increases the noise made by the motor,
often very considerably. The quoted CADR for a purifier is based upon its highest, and loudest,
setting and we’ve yet to find a purifier than you’d be comfortable sitting with for long in your home
when it’s running at full blast.
Secondly, if you blow air through any particle filter too fast, pollution that might otherwise be
trapped can be forced through, actually reducing the efficiency of the filter.
The effect of airflow on a gaseous filter of activated carbon is quite striking. Because these work not
by physically preventing pollution from passing through but by molecular attraction, the longer
pollution is inside the filter (known as ‘dwell time’), the more of it will be trapped. Slowing down the
airflow and using as thick a filter as possible greatly increases the effectiveness.
A good purifier will normally combine a particulate and a gas filter, but increasing the airflow to
remove particulates quicker can reduce the removal of gases. A purifier with a higher capacity will
clean faster at a lower speed and with less noise. It may cost more initially but there’s little point in
buying any solution if you end up not using it because of the noise.