Ventilation and Infiltration

Ventilation and infiltration relate to the movement of air within a building and exchange of air to outside, whether intentionally or unintentionally. They are both important considerations in creating healthy buildings whilst reducing heat loss.

Person holding anemometer

What is infiltration?

Infiltration or air leakage is uncontrolled ventilation whereby air is introduced into a building from outside. Infiltration occurs through gaps of cracks in the building fabric as well as around poorly sealed windows and doors. Unlike ventilation, infiltration is unintentional and unwanted as it will increase energy costs.

In winter months, infiltration causes heat loss as warm internal air is replaced by colder external air. This increase energy costs as the heating system will be active for longer and more often. In the summer months, there is the potential for infiltration to cause mould conditions as more humid air is introduced from outside.

Building regulations require that all new build houses are tested for airtightness and infiltration by sealing off all intended ventilation paths and pressurising the building. This allows the air permeability or air leakage to be measured - the greater the airtightness, the lower the infiltration level.

Air permeability and building regulations

Latest Part L building regulations require that new build houses have an infiltration or air permeability level of no more than 1.57 m3/h/m2 @ 4Pa or 8.0 m³/h/m² at 50Pa. These numbers are the maximum permitted volumetric flow rate of air per hour (m3/h), per square meter (m2) of building envelope area at the specified pressure difference.

Our Pulse Air Permeability Measurement System is an approved method for measuring these infiltration rates at low pressure (4Pa) for building regulation testing and compliance which can also be extrapolated to a 50Pa pressure test. Measuring infiltration and ventilation rates is also a very important part of the PAS 2035 standard, retrofitting buildings and adding home insulation.

What is ventilation?

Ventilation is the deliberate movement of air within a building using various ventilation strategies. It is intentionally added to buildings to ensure sufficient indoor air quality by supplying fresh air (oxygen) and removing carbon dioxide (CO2), odours, moisture and contaminants such as airborne chemicals (VOCs) or pollution (NOx).

A ventilation strategy and system must be carefully designed to ensure a healthy living environment. Too little ventilation can lead to poor indoor air quality potentially causing headaches, tiredness and difficulty concentrating for occupants. Whilst too much ventilation will lead to excessive heat loss and increased energy costs.

Types of ventilation include passive systems like natural ventilation and active systems such as controlled or mechanical ventilation which you can read about below.

Measuring infiltration and airtightness

Our unique air testing products are ideal for measuring the air leakage and infiltration rate of all buildings. They can be used for building regulation compliance and diagnostics purposes.

Pulse air receiver, controller and compressor

Pulse Air Permeability Testing

A pioneering approach to fabric air permeability measurement that releases a low-pressure pulse of air for realistic and accurate measurement of airtightness of buildings in seconds.

Learn more about Pulse Air Permeability Testing
Leak Checker Diagnostics Fan

Leak Checker Diagnostics Fan

A portable diagnostics fan that can help identify air leakage paths within buildings, helping to minimise infiltration, improve airtightness and reduce remedial work required to pass compliance testing.

Learn more about Leak Checker Diagnostics Fan

Natural ventilation

Natural ventilation is a method of supplying fresh air into a building by means of passive forces, typically by wind or differences in pressure between inside and out. In a typical house, natural ventilation will occur through air bricks in the fabric of the building or through trickle vents in windows. The building regulations define the minimum number of vents required in new build houses when relying on natural ventilation only.

More complex natural ventilation methods, such as passive stack ventilation or cross ventilation, rely on the buoyancy of air or prevailing winds to move air in and out of buildings. Multiple ventilation openings will exist so that warm air can escape through extract vents at a high level within the room, whilst new air is introduced using low-level inlet vents. This upward or cross-movement of air will remove stale air replacing it with fresh air.

Controlled ventilation

Controlled ventilation systems actively move air in and out of a building using fans to create either a positive or negative pressure difference between inside and out. All new build houses are required to have some form of controlled ventilation to meet building regulations.

In its simplest form, extract-only fans control the ventilation of kitchens and bathrooms by removing odours and moisture from cooking, cleaning or bathing that would otherwise cause damp, mould or condensation problems. In these situations, new air is introduced into a house via infiltration as well as the day-to-day opening and closing of external doors and windows.

Other active ventilation systems are fan/duct based and designed to work at a whole-house level. These include Positive Input Ventilation (PIV), Mechanical Extract Ventilation (MEV) as well as Mechanical Ventilation with Heat Recovery (MVHR).