Ventilators pump air from one side to another. It is important that the ventilators are pumping as much air as we expect them to do. If not, we are under- or over-estimating the effectiveness of our ventilators.

There are several factors that can influence the capacity of our ventilators.

- One of the most important ones is the negative pressure.
The ventilators pump the air outside of the building. This will create a negative pressure inside the house, which depends on the amount of air that is going through the inlets. At a high negative pressure, the ventilator will become less effective, and eventually the negative pressure can become so high that the ventilator is not moving air anymore, although it is still running.

The capacity drop due to negative pressure is specific for each ventilators. Some ventilators can handle negative pressure better than the others. It is important to know this when buying ventilators, as the amount of air that is moved will depend on the negative pressure they can handle.

- When a free flow of air towards or from the ventilator is obstructed, the capacity of the ventilator will go down, even when the ventilator is working normally. Shutters, blinds, bird wires, roofing material, etc., can all block the air flow and have an impact on the capacity of the ventilator. Check the real capacity of the ventilator if there is a suspicion that the flow of air is not totally unblocked.

- When the blades or the shutters and blinds of the ventilators get contaminated with dust and dirt, the capacity will go down as well. Regular maintenance must include the ventilators.