Air Purifier vs. Positive Pressure Fresh Air System – an unfair Battle?

by Achim Haug

We have made a comparison test between a positive pressure fresh air system (PPS) and a standalone purifier on the effectiveness of bringing the ambient PM 2.5 particles down.

A positive pressure fresh air system takes air from outside, filters it through a HEPA filter and pumps it into the room. Thereby pressurizing the room and thus preventing dirty air from entering the room.

To make the comparison meaningful we chose similar specifications on both the positive pressure system and the air purifier.


  • 220m3/h airflow
  • 30w


  • 280m3/h airflow
  • 30w

So the purifier is slightly more powerful in regards to airflow.

The comparison was done in a 32m2 room with the above PPS system permanently installed.

Timeline of the experiment:

  • 10:10pm: PPS System was switched off and purifier was switched on (to maximum setting)
  • 04:15am: PPS System was switched on
  • 04:45am: Purifier was switched off

As we can see from the graph, once the positive pressure system was switched off, polluted air entered the room through small air gaps. It increased for approximately 1 hour until it reached equilibrium with the purifier at around 50μg/m³.

The standalone purifier was able to reduce the ambient PM 2.5 values by about 75%. We can see some correlation with the outside PM 2.5 values so we can assume that the indoor pollution would always fluctuate depending on the outside values.

On the other hand with the positive pressure system switched on, we can see that the PM 2.5 values stay permanently at zero and there is no correlation with the outside air quality. This is because the positive pressure inside the room prevents any dirty air from entering the room.

So we see that the positive pressure system has a number of advantages:

  • The pressurization can keep PM2.5 at zero no matter what the outside air quality is
  • It can achieve this with a lower airflow
  • By constantly pumping fresh air into the room, CO2 levels will remain low

To learn more about positive pressure systems, read our more detailed article on positive pressure system.

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