EN 13779

The new European standard EN 13779:2007 focuses on achieving a comfortable and healthy indoor environment in all seasons with acceptable installation and running costs. It is now a national standard in all countries. It specifies the required filter performance in a system to achieve good Indoor Air Quality (IAQ) taking into consideration the outdoor air. The outdoor air is categorized in 3 levels, from ODA 1 where the air is pure except for temporary pollution such as pollen, up to ODA 3 with high concentrations of both gases and particles. The particulate matter refers to the total amount of solid or liquid particles in the air. Most outdoor air guidelines still refer to PM10 (particle diameter up to 10 μm). However, for the purpose of health protection, there is growing acceptance that emphasis should be placed on particles far smaller than 10 μm. The gaseous pollutants refer to concentrations of CO2, CO, NO2, SO2 and VOCs.

The table below indicates typical concentration levels in outdoor air, together with a suggestion on how to categorize the quality.

Concentration levels of outdoor air

Description of air qualityConcentration levels*Category of outdoor air

CO2 (ppm) CO2(mg/m2) NO2 (μg/m2)


Rural areas with no significant sources 350 < 1 5 - 35 < 5 < 20 ODA1
Smaller towns 400 1 - 3 15 - 40 5 - 15 10 - 30 ODA2
City centres 450 2 - 6 30 - 80
10 - 50 20 - 50 ODA3

Note that in most cities, what is termed a “normal concentration level” for particulates actually falls in the upper range (poor quality) for outdoor air i.e. ODA 2 or ODA 3. For particulate matter, the World Health Organization has established a target to reach an annual mean of PM10 below 40 μg/m3. This target has not yet been reached. In other words, most people in Europe spend most of their time in areas where the outdoor air must be categorized as ODA 2 or ODA 3. It can be readily concluded that the application of appropriate filtration is critical for health concerns.

The new standard classifies the indoor air quality from IDA 4 (low IAQ) up to IDA 1 (high IAQ). One traditional but limited method for determining the IAQ is to study the CO2 levels. CO2 is the product of human respiration. It is a good indicator of effective ventilation, but not of absolute air quality. Another established method for spaces with human occupancy is to specify the rate of external air added for each person. Values of this type are often used to size the ventilation system. The table below lists typical ranges for CO2 levels and recommended rates for added external air to achieve different categories of indoor air quality. Note that neither method takes into account the particulate and gaseous pollutants brought into the building with the external air.

Classification of indoor air quality

CategoryDescriptionCO2 –level above level of outdoor air (ppm) Typical rangeRate of outdoor air
Typical range, non-smoking area
IDA 1 High IAQ < 400 >54
IDA 2 Medium IAQ 400 – 600 36 - 54
IDA 3 Moderate IAQ 600- 1000 22 – 36
IDA 4 Low IAQ > 1000 < 22

Filter recommendations according to EN 13779

After the Outdoor Air Quality has been categorised, EN 13779 clearly specifies the filter class that is required to achieve preferred Indoor Air Quality. The filter classes are specified inaccordance with EN 779:2012. The EN 13779 standard is clear, when you require a decent IAQ (IDA 1 or IDA 2) and you are situated in a city environment, not only is F9 required as the final filter, but also a gas filter (GF) is required to protect against gaseous (molecular) pollutants!

Outdoor Air QualityIAQ (Indoor Air Quality)
IDA 1 (High) IDA 2 (Medium) IDA 3 (Moderate) IDA 4 (Low)
ODA1 F9 F8 F7 M5
ODA2 F7 /  F9 M6 / F8 M5 / F7 M5 /  M6
ODA3 F7 / GF / F9 F7 / GF / F9 M5 / F7 M5 / M6
GF) gas filter


  • In a city environment, it is recommended to use a molecular filter (gas filter). It is also a good solution in an area of categories ODA 3. The gas filter should be combined with a downstream F8 or F9 particulate filter. 
  • For hygienic reasons, it is recommended to use two-stage particle filtration: 
    -  Minimum M5, but preferably F7 in the first step.
    – Minimum F7, but preferably F9 in the second step.
    – If there is only one filtration step, the minimum requirement is F7.
  • For recirculation air, at least M5 quality must be used in order to protect the system. Preferably the same filter class as the main external air stream should be used.
  • For protecting the extract and exhaust systems, use at least class M5.
  • Regardless of filter class used, the efficiency must not deteriorate below defined values. Always look for the untreated (discharged) efficiency. The untreated (discharged) efficiency is reported when a filter is tested according to the current valid European standard EN 779:2012, which replaced the former EN 779.
  • The interval of filter replacement must not be selected only on the basis of economical optimisation. Hygiene issues must also be taken into account. Three limits must be considered, and the one that is reached first will determine the time for replacement: final pressure drop, time installed and time in operation.
    – For first step filters: 2000 hours operation or maximum 1 year installed or when the final pressure drop is reached.
    – For second or third step filters: 4000 hours operation or maximum 2 years installed or when the final pressure drop is reached.
    – For exhaust- and recirculated air filters: 4000 hours operation or maximum 2 years installed or when the final pressure drop is reached.
  • To avoid microbial growth, the plant should be designed so that the relative humidity (R.H) always stays below 90% and so that the average R.H for three days is less than 80% in all parts of the system, including the filters.
  • Gas filters do not change pressure loss during normal operation. In the absence of a definitive statement within EN 13779, Camfil Farr recommends to change IAQ gas (molecular) filters after 1 year installed or 5000 hours operation.

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