What is Ventilation?

Ventilation is the bedrock of good indoor air quality. Its function is to remove stale air from a building and to introduce outdoor air into the space. Part F of the Building Regulations makes ventilation a legal requirement for buildings, and there are several approaches used, depending on the type and design of a building.

Indoor air quality and ventilation - what are they and why do they matter?

You have probably heard the term ‘ventilation’ a lot in recent years, particularly in relation to reducing the presence of Covid 19 from indoor spaces. But what is ventilation and why does it matter so much? Ventilation is the process of removing stale air from a building and replacing it with air from outside. There are several ways to ventilate buildings according to factors such as building size and type.

Benefits of good ventilation 

The main benefit of ventilation is that it supports good indoor air quality by flushing out airborne pollutants and contaminants from indoor spaces. However, the air that is introduced into the building must be clean and free of pollutants. In fact, ventilation is now regarded as one of the most important investments building owners and managers can make for the health and productivity of occupants.

Natural Ventilation and Mechanical Ventilation  

Natural Ventilation 

Natural ventilation supplies air to and removes air from a building without the use of mechanical equipment such as fans. This can include simply using the windows in the building to open when required.

Some buildings are designed to use natural processes such as cross ventilation (where air is ‘pulled’ through a building by natural air movement and buoyancy).

Natural ventilation systems can include features such as trickle vents above windows; solar chimneys to draw warm air up and out of a building (pulling in cooler air at a lower level); or wind towers.


  • No mechanical parts which reduces system energy use, and therefore energy costs.
  • Few moving parts also reduces the need for maintenance.
  • Lower embodied carbon (compared to mechanical ventilation systems.
Natural Ventilation

Mechanical ventilation (and MVHR)

Mechanical ventilation makes use of fans and other equipment to move air into and out of a building. Ventilation systems are often driven by equipment such as air handling units (AHUs) connected to ducts which run throughout the building. Some systems use the energy from warm, extracted air to pre-heat air entering the building - known as mechanical ventilation with heat recovery (MVHR).

The benefit of this approach is that MVHR systems simultaneously extract stale air from a building and provide a supply of filtered air. While doing this, the units simultaneously recover valuable heat energy for maximum efficiency. MVHR units can also include filtration of pollutants such as NOx and particulate matter to improve IAQ. The filter specification should be reviewed critically as many designs are supplied with, or only capable of running low-efficiency filtration. Some units can be equipped with carbon filters to remove a portion of gas-phase pollutants such as nitrogen oxides


  • Ventilation rates are controllable and predictable
  • MVHR is an energy efficient approach to ventilation
  • Mechanical ventilation systems can be more easily retrofitted to existing buildings
Mechanical Ventilation

How to improve ventilation?

Building Regulations recognise the importance of ventilation in homes. In England and Wales, Part F (Volume 1) of the Building Regulations (2021) 6 covers ventilation in dwellings and requires that ‘adequate’ ventilation is provided in all homes, whether they are new-build or existing.

Scotland’s Building Standard Technical Handbook (Annex 3) also deals with ventilation, stating that: “Ventilation of a dwelling is required to maintain air quality and so contribute to the health and comfort of the occupants.” In addition, control of humidity is specifically required to prevent mould. In Northern Ireland, Part K of the Building Regulations covers the issue of ventilation, and again the requirements are to limit the accumulation of moisture that could lead to mould growth.

Although there are different regulations on ventilation across the UK, they generally agree on the primary purposes and methods of ventilation for homes. The three main ventilation strategies are:

Extract ventilation

Applied in rooms where water vapour or pollutants are most likely to be released, for example, bathrooms and kitchens. Extract fans can be intermittent or continuous

Whole dwelling ventilation

Provides outdoor air to the home, diluting and dispersing indoor pollutants and water vapour (which hasn’t been extracted by other means)

Purge ventilation

Removes high concentrations of pollutants and water vapour. It is used intermittently and required only occasionally, for example, to remove fumes from painting. It can be delivered simply by opening windows or doors.

World Ventil8 Day - 8th November

Taking place every year on 8th November, World Ventil8 Day aims to raise awareness of the importance of ventilation as a crucial part of enabling health and wellbeing of people. It also seeks to recognise and celebrate the ventilation and indoor air quality community. We want you to be part of it, whether you are a ventilation professional or someone with a passion for fresh air in your buildings.

As a champion of the importance of ventilation in improving our health and wellbeing, BESA are a founding member of World Ventil8 Day.

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