Ventilation grille dimensions and other system requirements

Within the process of renewing the air in a building (ventilation), grilles play a fundamental role. They allow the flow of air to pass through. If the purpose of the grille is to supply a certain amount of air into the spaces, we refer to it as admission openings. Conversely, if the aim is to expel stale air outside, we refer to it as extraction openings. Regardless of their purpose, do you know what dimensions these grilles should have and what technical specifications they must meet?

Dimensions of ventilation grilles (supply, extraction, passage, and mixed)

According to the Technical Building Code, in its section HS 3 Air Quality, the effective surface area, expressed in cm2, of the ventilation grilles for each space must be as follows (always choosing the highest value):

For admission openings

4 × qv or 4 × qva

For extraction openings

4 × qv or 4 × qve

For passage openings

70 cm2 or 8 × qvp

For mixed openings (those that can serve both for admission and extraction)

8 × qv
Where, on one side, qv is the minimum ventilation flow required for the space, expressed in l/s, according to table 2.1 of the document which establishes the minimum flows for each of the rooms in the dwelling. On the other hand, the ventilation flows calculated based on a balanced calculation between the supply flow and the extraction flow, expressed in l/s, are qva (the ventilation flow relevant to each admission grille of the space), qve (the ventilation flow relevant to each air extraction grille of the space), and qvp (the ventilation flow corresponding to each passage grille of the space).

Dimensions of the extraction ducts

Section of the extraction ducts for hybrid ventilation

The section of the extraction ducts for hybrid ventilation is derived from the table 4.2 of section HS 3 of the document. The parameters to be considered are the following:

• The airflow in the duct run, expressed in l/s: qvt. This airflow qvt is the result of adding all the extraction flows from each of the extraction grilles that connect with the extraction duct.

• The type of draft (“upward movement of air between two points produced by the existing temperature difference between them”), depending on the number of floors that the duct spans and the thermal zone in which the building is located.

In the case of collective ducts, the section of each bifurcation must be at least equal to half of the main duct’s section.

Section of the extraction ducts for mechanical ventilation

In the case that the ducts are located adjacent to a habitable space (unless they are located on the roof or in conduits that meet the requirements of Basic Document HR), the section of each branch of the duct must be at least two and a half times the airflow in the duct run (qvt). If the extraction duct is located on the building’s roof, the duct section must be at least one and a half times this qvt.