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About Trickle Ventilators

Why are trickle ventilators needed?

Why are trickle ventilators needed?

This has long been a controversial and puzzling question in the fenestration market since its introduction.

The typical question has been -

"Why having developed thermally efficient window systems do we then rout a hole in the top?"

Over the last few revisions of the regulations, the airtightness of buildings has become an increasing issue. On the one hand there has been a drive to improve the thermal efficiency of windows whilst reducing energy consumption, as we build greener buildings. The consequence has been that as dwellings are made more airtight and internally generated pollutants affect disproportionately indoor air quality. This may cause adverse health effects unless unobtrusive background ventilation is installed.

Background ventilation is therefore necessary to provide a healthy indoor environment for the occupants. The primary purpose of trickle ventilation is to remove polluted indoor air from a building and replace it with ’Fresh’ outside air. Background Ventilation is a key product for a healthy living environment. These small trickle ventilators are designed to deliver controllable whole room ventilation.

Background ventilation using trickle ventilators provides;

Background ventilation using trickle ventilators provides;

Low Co2 footprint

This system consumes no electrical power once installed.


Installation foot prints prevent intrusion into the property. Whilst allowing constant ventilation even when the window is locked, as even locking handles can be a risk.


Ventilators are designed to deflect the airflow to minimize draughts.

Cost effective

The lowest cost route for provision of background ventilation without the need for air bricks and no ongoing electricity costs.

Cleaner building designs

As background ventilation is delivered through the window reveal no additional means of ventilation need be installed.

Noise reduction

A property in a noisier location, E.g. near a busy road or airport. Trickle ventilators provide ventilation without the need to open the windows, reducing noise levels.

Condensation reduction

Some properties may have an existing problem with condensation especially in colder weather. Fitting windows with suitable trickle ventilation may improve the problem and potential risk of mould growth is reduced, which could minimise damage to internal surfaces.


Fresh may reduce health problems, E.g. Asthma sufferers. Whilst also helping to manage background air the levels of pollutants such as carbon monoxide and carbon dioxide. The building regulations require the number of inhabitants in a property to be a consideration when planning a ventilation requirement.

24 hours operation

Even at night and whilst you are on holiday they can still operate.

Controlled heat loss

By using calculated background ventilation the need for purge and extraction of warm air is managed. Background ventilation can assist with air temperature movement between the habitable room and the atmosphere.

Thermal comfort

Trickle vents are designed and located (typically 1.70 m above floor level) to control air movement (draughts) in habitable rooms.

Other ventilation types include ‘Purge’ and ‘Extraction’ is mechanical and is used locally within a building typically for kitchens and bathrooms where pollutants and water vapour are removed to prevent spreading throughout the building.

What are the Free and Equivalent areas of background trickle ventilators?

What are the Free and Equivalent areas of background trickle ventilators?

Equivalent area (EQA) is used instead of free area for the sizing of trickle ventilators as it is a better measure of the ventilators air flow performance.

Free area is the geometric cross sectional area of the opening of the ventilator. This however may not accurately reflect the air flow performance achieved by the ventilator. The more complex and/or restricted route of the air flow through the ventilator, the less air can flow through it.

Therefore, two separate ventilators with equal free areas may have different ventilation performance.

In order to calculate the EQA, the F1 Approved document uses a method defined in European Standard, BS EN 131 41-1 :2004 (Clause 4), for measuring the EQA of background ventilators.

EQA cannot be assessed on site, so it will be difficult to demonstrate that trickle ventilators have the correct EQA, so it is preferable to use ventilators which have the EQA (mm² at 1 Pa pressure difference), marked on the ventilator in a visible location, in the room to be ventilated, when installed.

The EQA is determined in accordance with BS EN 13141:2006 Part 1 “Ventilation for Buildings - Performance testing of components/products for residential ventilation - Part 1: Externally and internally mounted air transfer devices”.

Clause 4.1 defines the test; “Flow Rate/Pressure” of BS EN13141 - 1 at pressures between 1 and 100Pa. The equivalent free area test calculates a value in mm² at a pressure difference of 1Pa.

The EQA is calculated using characteristic K at six pressures to measure the airflow. At 1Pa pressure difference the K value equals the corrected volume air flow rate Qvcor in l/s. This is multiplied by the coefficient C to give the equivalent free area in mm².

This information is for guidance only and is based upon Approved Document F1 at the time of publication.

Demonstrating this difference below is the geometric and EQA values of our modular ventilator range.


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Glazpart Ltd
Wildmere Industrial Estate
OX16 3JU

Tel: +44 (0)1295 264533