Learn how to read Supply Air, Extract Air, Supply / Extract, AIRFLOW, THIS SIDE UP, F7 and ISO 16890 markings on ventilation filters and install them correctly.
Ventilation filter markings tell you where the filter belongs, which direction it should face and which filtration class you are installing. Correct installation helps maintain the intended filtration performance, airflow and normal filter service life.
A ZenAero filter may include several different markings. Read all of them together rather than relying on the filter class or appearance alone.
Example product code: ZA-1301-F7. The code identifies the exact filter version and helps you order the same replacement again.
Filter class note: F7, M5 and G4 are legacy EN 779 designations still widely used in the market. Current labels may also show the ISO 16890 classification, for example ePM1 60% or ISO Coarse.
The position marking tells you where the filter belongs in the ventilation unit.
Install the filter on the fresh outdoor-air / supply side.
Install the filter on the air-extract side from the building.
The filter can be used in either position where the unit configuration allows it.
If the F7 filter is marked Supply Air and the G4 filter is marked Supply / Extract, install F7 on the supply side and G4 on the extract side. A G4 filter that physically fits either slot is not automatically interchangeable with the dedicated F7 supply filter.
The arrow shows the direction in which air should pass through the filter. Install the filter with the arrow pointing in the airflow direction.
On many residential heat-recovery units, air moves from the duct side towards the heat exchanger closer to the centre of the unit. Treat this only as a clue: always check the markings on the unit or the manufacturer’s instructions.
This is a physical orientation mark, not an airflow arrow. Install the filter with the THIS SIDE UP arrow pointing upwards.
This marking is used on filters for units such as Zehnder ComfoAir Q 350 / 450 / 600 and other configurations that require a specific upright orientation.
In many ventilation units, the supply and extract filters have different dimensions or shapes. This makes it relatively difficult to install the wrong filter in the wrong slot, but the printed markings should still be checked before installation.
Follow both pieces of information: use the correct position and install each filter according to its airflow arrow.
This is where the markings become especially important. Some ventilation units use filters with very similar or identical external dimensions but different filtration efficiencies. The G4 filter may physically fit either slot, but that does not mean the F7 and G4 filters should be installed interchangeably.
F7 → Supply Air
G4 → Extract Air
The F7 and G4 filters are very similar in size, so checking the label is essential.
For these filters, the arrow points from the duct side towards the centre of the ventilation unit.
Siber DF EVO compatible F7 + G4 set →
Zehnder EVO compatible F7 + G4 set →
Mitsubishi Electric SVL compatible F7 + G4 set →
The same position rule matters on other F7 + G4 sets where the filters look similar. Existing compatible sets include Salda Smarty 2XP 1.1 / 1.2 and Vaillant recoVAIR VAR 260/4 and 360/4.
First check the ventilation unit itself. Manufacturers often mark the filter positions next to the slots using airflow symbols, filter classes, supply / extract symbols, arrows or labels in the service compartment.
If the positions are not clearly marked, check the manufacturer’s manual. The outdoor-air / supply duct is also frequently insulated, which can help identify the supply side, but duct insulation is a clue rather than a replacement for the manufacturer’s instructions.
Filters that physically fit into both slots should not automatically be treated as interchangeable. Always check their markings first.
If you have an F7 + G4 set where F7 is marked Supply Air and G4 is marked Supply / Extract, install F7 on the supply side and G4 on the extract side.
The filter is intended for the fresh outdoor-air / supply side of the ventilation unit.
The filter is intended for air extracted from inside the building.
The filter itself can be used in either a supply or extract position where the ventilation unit or filter configuration requires it. It does not mean that every filter in the set is interchangeable.
If the F7 filter is marked Supply Air and the G4 filter is marked Supply / Extract, install F7 on the supply side and G4 on the extract side.
The arrow indicates the direction in which air should pass through the filter. Install the filter with the arrow pointing in the direction of airflow.
It is an orientation mark, not an airflow arrow. Install the filter with the THIS SIDE UP arrow pointing upwards.
Stop before using the filter. Check the markings next to the filter slot and the manufacturer’s manual, or contact ZenAero Support with the unit model, a photo of the filter slot and the filter dimensions.
Send us the ventilation-unit model, a photo of the filter slot and the filter dimensions.
